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  Virus Information
   

1. What is a computer virus?
A computer virus is a program designed to replicate itself by infecting executable files or files in the system areas of hard and floppy disks. Viruses generally operate without the knowledge or desire of a basic computer user.

2. What kind of files can spread viruses?
Viruses can infect any type of executable code, not just files commonly called 'program files'. For example, some viruses infect executable code in the boot sector of floppy disks or in the 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 is also possible for some virsus to infect HTML documents containing JavaScript or other types of executable code.

Since virus code must be executed before it has any effect, files that your computer treats as pure data are safe. This includes multiple types of media such as; .gif, .jpg, .mp3, .wav, etc., as well as plain text documents .txt. For example, just viewing picture files won't infect your
computer with a virus. The virus code has to be in a form, such as an .exe program file or Word .doc file, that the computer will actually try to execute.

3. How do viruses spread?
When you execute a program that's code is infected with a virus, the virus code will also run and try to infect other programs. This can happen on the same computer or computers attached via a LAN (Local Area Network). Once the virus has successfully infected new files those new files then continue on trying to infect more programs.

When you share a copy of an infected file with other computer users, running the file may also infect their computers; and files from those computers may spread infect to yet more computers.

If your computer is infected with a boot sector virus, the virus tries to write copies of itself to the system areas of floppy and hard disks. Then then infected floppy disks may infect other computers that boot from them, and the virus copy on the hard disk will try infect still more floppies.

Some viruses, known as 'multipartite' viruses, can spread both by infect files adn by infecting the boot areas of floppy disks.

4. 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.

5. What is a Trojan horse program?
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.

6. What's the story on viruses and E-mail?
You can't get a virus just by reading a plain-text E-mail message. 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).

In order to activate a virus or Trojan horse program, your computer has to execute some type of code. This could be a program attached to an E-mail, a Word document you downloaded from the Internet, or something received on a floppy disk. There's no special hazard in files attached to E-mail messages: they're no more dangerous than any other file.
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