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Computer Virus Information Guide
Q: What is a virus?
A computer virus is a program or script that was created to cause damage
or disruption on a computer and then spread to other machines.
They are normally added onto, or disguised as useful executable files,
or screen saver files. One of the main goals of a virus is to operate without
a computer user knowing they are there.
Q. What kind of files can spread viruses?
Viruses have the potential to infect any type of executable code, not just the files that are commonly called 'program files'. For example, some viruses infect executable code in the boot sector of floppy disks or in system areas of hard drives. Another type of virus, known as a 'macro' virus, can infect word processing and spreadsheet documents that use macros.
It's possible for HTML documents (web pages) containing JavaScript or other types of executable code to spread viruses or other
nasty things.
One good thing is that viruses are type specific. That is they
can't go from being a Macro virus to being a boot sector virus.
This helps in keeping them under control to some extent.
Since virus code must be executed (you have to start them up), files that
are pure data are safe. This includes graphics and sound files such as .gif, .jpg, .mp3, .wav, etc., as well as plain text in .txt files. For example, just viewing picture files
CAN'T infect your computer with a virus. The virus code has to be in a form, such as an .exe program file or a Word .doc file, that the computer will actually try to execute.
The most common file types that CAN have viruses are:
- .exe (windows executable files - programs)
- .bat (batch files. A series of commands that the system does
automatically)
- .pif
- .scr (Screen Saver files)
- .doc (Word document can contain Macros that can carry virii)
- .xls (excel spreadsheets - same as above).
Q. How do viruses spread?
When you execute program code that's infected by a virus, the virus code will also run
and do it's work. It will do two things 1) try to do its nasty
work, 2) try to spread and infect other files so that it will live on,
and possibly spread to other machines. The newly infected programs will try to infect yet more programs. When you share a copy of an infected file with other computer
users (via email, or floppy disks for example), running the file may also infect their
computers and so on down the line.
If your computer is infected with a boot sector virus, the virus tries to write copies of itself to the system areas of floppy disks and hard disks. Then the infected floppy disks may infect other computers that boot from them, and the virus copy on the hard disk will try to infect still more floppies. Some viruses, known as 'multipartite' viruses, can spread both by infecting files and by infecting the boot areas of floppy disks.
Today the most common way viruses spread it through email documents
containing infected files that are attached with the email. Smart
viruses will even take over your email system, attach copies of the
virus to email messages, and then automatically send them out to
EVERYONE on your email list. Automatically.
Can you see why it is important for you to protect your computer with
top quality, current virus protection?
Q. What do viruses do to computers?
Viruses are software programs, and they can do the same things as any other programs running on a computer. The actual effect of any particular virus depends on how it was programmed by the person who wrote the virus. Some viruses are deliberately designed to damage files or otherwise interfere with your computer's operation, while others don't do anything but try to spread themselves around. But even the ones that just spread themselves are harmful, since they damage files and may cause other problems in the process of spreading. Note that viruses can't do any damage to hardware: they won't melt down your CPU, burn out your hard drive, cause your monitor to explode, etc. Warnings about viruses that will physically destroy your computer are usually hoaxes, not legitimate virus warnings.
Q. What is a Trojan horse?
A type of program that is often confused with viruses is a 'Trojan horse' program. This is not a virus, but simply a program (often harmful) that pretends to be something else. For example, you might download what you think is a new game; but when you run it, it deletes files on your hard drive. Or the third time you start the game, the program E-mails your saved passwords to another person. Note: simply downloading a file to your computer won't activate a virus or Trojan horse; you have to execute the code in the file to trigger it. This could mean running a program file, or opening a Word/Excel document in a program (such as Word or Excel) that can execute any macros in the document.
Q. What's the story on viruses and E-mail?
You can't get a virus just by reading a plain-text E-mail message or Usenet post. What you have to watch out for are encoded messages containing embedded executable code (i.e., JavaScript in an HTML message) or messages that include an executable file attachment (i.e., an encoded program file or a Word document containing macros). However,
most email is now being sent as HTML format, and NOT plain text.
This makes it very easy for nasty people to put nasty code into an email
message. This is particularly true with Windows email programs like
Outlook and Outlook express that by default display (in a pane) an email
message as it comes in. This AUTOMATICALLY starts the code - and a
virus - if it is there!
Proper virus protection scans and quarantines all incoming email messages
for virus and trojan horse threats.
Q. How can reduce the chance of getting a virus through E-mail?
- Scan ALL file attachments carefully with up-to-date anti-virus
software
- Disable Automatic display/Reading of email messages in your email
software
- Delete any unexpected email attachments without question, especially
if you don't know who sent it to you, or you were not expecting a file
attachment.
Remember, a virus WANTS to be secret and WANTS to spread. Just because an E-mail
came from someone you know, does NOT mean the file is safe or even that
they actually sent it themselves.
The best thing to do is get current antivirus software like we review
on the other pages, and tell all your friends, family and colleagues to
do the same. It is only unprotected (or poorly protected)
computers that can be infected and spread a virus. This means
that any computer without protection, is part of the problem, and part of
the cause of viruses spreading.
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