Virus, Worm or Trojan Horse?:
Virus
A virus is a malicious computer program that spreads itself by infecting other programs on the same computer. At their worst, viruses can do serious damage - erasing your files or even your whole disc drive. Some are less serious. A true virus cannot spread to a different computer unless an infected file is introduced, e.g. on a floppy disc or by an e-mail attachment, and opened.
Worm
A worm is similar to a virus in that it propagates itself but unlike a virus, a worm can spread automatically over a network from one computer to another. This is done by taking advantage of automatic file sending and receiving features - for example by sending itself to everyone in an e-mail address book.
Trojan horse
This is a general term for a program that appears to offer something desirable, for example a free game, movie or music file, but actually contains a hidden worm or virus. When you run the program, the worm or virus is activated. At their worst, trojans can present a serious security threat - sending your credit card numbers or passwords to a stranger, or giving remote access to your computer.
Note for Win XP users: It is highly recommended that you download Windows Service Pack 2, as it includes important security updates.
Avoiding Viruses:
Some kind of anti-virus software is essential. It is also vital to make sure that you keep up-to-date with regular updates since new viruses are appearing all the time. (See Resources below for links to some anti-virus sites.) Unfortunately, you cannot rely solely on anti-virus programs as, to some extent, they are always catching up with the latest viruses.
Be careful when downloading files from the Internet. Make sure that the source is a legitimate and reputable one. If you're uncertain, don't download the file at all or download it to a floppy disc and test it with your anti-virus software.
Don't open a file attached to an e-mail unless you know what it is. Many viruses replicate themselves and spread through e-mail.
Back up your data regularly so that, if the worst happens and a virus destroys your files, you can replace them with your back-up copy.
Do I need a Firewall?:
A Firewall is hardware and/or software that limits access to a computer over a network or from an outside source. Firewall programs are intended to counter the threat of trojans which install a "backdoor" program on to your computer that can then be exploited remotely. The firewall blocks external access and backdoor communications to your computer. (See Resources below for links to some personal firewall sites.)
Although important as a barrier, a firewall cannot stop you from downloading the trojan that installs the backdoor in the first place.
Windows XP has a firewall as part of the operating system. Although currently very basic, it is worth turning the Windows firewall on - it is better than having no protection at all.
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