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What Are Computer Viruses?

Types of Infection

  • Viruses
  • E-mail Viruses
  • Worms
  • Trojan Horses

What Is A Virus?

  • Viruses - A virus is a software program that is capable of replicating with little or no user intervention, and the replicated programs also replicate further. Viruses piggyback on real programs. For example, a virus may attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs as well, and it has the opportunity to reproduce by attaching to other programs. The purpose of a virus can be anything from erasing files, formatting your hard drive, to replacing text in your document. Viruses are often disguised as games or images with clever titles such as "Pictures of ME".
  • E-mail Viruses - An email virus moves around in e-mail messages, and usually replicates itself by automatically mailing itself to the people in the victim's e-mail address book.
  • Worms - A worm is a virus that spreads by creating duplicates of itself on other drives, systems, or networks. Worms may send copies of themselves to other computers across network connections, through e-mails, through infected web pages, or through instant messages.
  • Trojan Horses - This program may claim to do one thing (such as claiming to be a game) but instead does damage when you run it. Trojan horses are not technically viruses, since they do not replicate.

How Do Viruses Spread?

When you execute program code that is 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.

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

What Do Viruses Do To Computers?

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 interfere with your computer's operation, while others only spread themselves around and may cause damage to your computer in the process of spreading.

Tips On Avoiding Viruses:

  • Install antivirus software, update regularly, and use it regularly.
  • Do regular backups. If you contract a virus it may be the only way to recover your data. Ideally, you should backup your entire system on a regular basis, however if this is not practical, at least backup files that you can't afford to lose or that would be difficult to replace: documents, bookmark files, address books, important emails, etc.
  • When possible, avoid e-mail attachments both when sending and receiving e-mail.
  • Never open email attachments with the file extensions VBS, SHS, or PIF. These extensions are almost never used in normal attachments but they are frequently used by viruses and worms.
  • Never open attachments with double file extensions such as NAME.BMP.EXE or NAME.TXT.VBS.
  • Disconnect your network or modem cable when you're not using your computer-or just power it down.
  • If you feel that an e-mail you get from a friend is strange (if it is a foreign language or it just says odd things) double check with the friend before opening any attachments.
  • When you receive e-mail advertisements or unsolicited e-mail, do not open attachments.
  • Avoid attachments with sexual file names.
  • Do not trust the icons of attachment files. Worms often use executable files which have an icon resembling icons of picture, text, or archive files to fool the user.
  • Never accept attachments from strangers in online chat systems.
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