CompTIA A+ Certification

Viruses are little programs that can wreak havoc on a computer and its data. Many viruses are simple annoyances, but some of them can cause irreparable harm to files. Viruses can be caught from various sources including shareware, files downloaded from the Internet, software from unknown origins, and bulletin boards.

There are several different types of viruses:

• File infectors attach themselves to executable files and spread to other files when the program is run.
• Boot sector viruses replace or hide inside the master boot record or boot sector on a floppy disk and write themselves into memory any time the computer is booted.
• Trojan horses are disguised as legitimate programs, but harm the system when loaded.
• Macro viruses attach themselves as executable code inside a document such as a Microsoft Word document and run when the document is opened.
• Polymorphic viruses modify themselves over time and replicate new forms. This makes them both unpredictable and harder to detect.

There is no complete defence against the threat of viruses, but virus detection and remedial software should be used to minimize the threat. Anti-virus software can be purchased and downloaded from the Internet or obtained through computer retail outlets. Because viruses change rapidly and new ones appear regularly, you should purchase anti-virus software that provides free or low-cost regular upgrades. The anti-virus software must be compatible with the version of Windows on the computer.

In addition to anti-virus software, you could also disable boot-sector writes if the computer has a BIOS setting that allows you to; be careful when reading a floppy disk of unknown origin or using your disk on an unfamiliar computer; and use extreme caution on the Internet when you download files, especially if they come from sources other than a manufacturer's Web site.