1. What is a computer virus?
Computer virus is a program designed to spread itself by first infecting executable files or the system areas of hard and floppy disks and then making copies of itself. Viruses usually operate without the knowledge or desire of the computer user.
2. 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'
Since virus code must be executed to have any effect, files that the computer treats as 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 won'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.
3. How do viruses spread?
When you execute program code that's infected by a virus, the virus code will also run and try to infect other programs, either on the same computer or on other computers connected to it over a network. And the newly infected programs will try to infect yet 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 the infection 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 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.
4. Where is the virus located?
Boot sector viruses alter the program that is in the first sector (boot sector) of every DOS-formatted disk. Generally, a boot sector infector executes its own code (which usually infects the boot sector or partition sector of the hard disk), and then continues the PC bootup (start-up) process. In most cases, all write-enabled floppies used on that PC from then on will become infected.
5. 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 bout viruses that will physically destroy your computer are usually hoaxes, not legitimate virus warnings.
6. 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.
7. How can I avoid infection?
There is no way to guarantee that you will avoid infection. However, the potential damage can be minimized by taking the following precautions:
* Make sure you have a clean boot disk - test with whatever (up-to-date!) antivirus software you can get hold of and make sure it is (and stays) write-protected. Boot from it and make a couple of copies.
* Use reputable, up-to-date and properly-installed anti-virus software regularly. (See below) If you use a shareware package for which payment and/or registration is required, do it. Not only does it encourage the writer and make you feel virtuous, it means you can legitimately ask for technical support in a crisis.
* If you use a shareware/freeware package, make sure you have hard copy of the documentation *before* your system falls apart!
* Always run a memory-resident scanner to monitor disk access and executable files before they're run.
* Scan pre-formatted diskettes before use.
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