Virus Prevention Guidelines

Make sure your computer runs anti-virus software. If not, buy and install it immediately.

Even if you have this software, it must be updated regularly, as new viruses appear daily. Configure the programs to automatically download updates, making it easy to stay protected. Otherwise, periodically download the updates manually.

DO NOT OPEN an e-mail attachment unless you know who sent it. Even then, it's not totally safe, as a sneaky virus that has infected a friend's computer can access the e-mail address book, send a message to everyone, and attach itself. To be completely safe, scan the attachment with your anti-virus software BEFORE you open it.

If you receive a suspicious message, delete it immediately from your Inbox. When you delete a message, however, it's still on your system. Go into the Deleted Mail folder and delete the message again to permanently remove it from your computer.

Regularly back up your files. Should your system become infected, you won't lose valuable data.

Warning Signs of Virus Infection

Your computer starts running sluggishly.

It shuts down unexpectedly or crashes frequently.

It experiences memory problems or runs out of disc space.

Unusual files or directories appear on your system.

Strange messages appear on your screen.

How Computer Viruses Work

Strange as it may sound, the computer virus is something of an Information Age marvel. On one hand, viruses show us how vulnerable we are -- a properly engineered virus can have a devastating effect, disrupting productivity and doing billions of dollars in damages. On the other hand, they show us how sophisticated and interconnected human beings have become.

For example, experts estimate that the Mydoom worm infected approximately a quarter-million computers in a single day in January 2004. Back in March 1999, the Melissa virus was so powerful that it forced Microsoft and a number of other very large companies to completely turn off their e-mail systems until the virus could be contained. The ILOVEYOU virus in 2000 had a similarly devastating effect. In January 2007, a worm called Storm appeared -- by October, experts believed up to 50 million computers were infected. That's pretty impressive when you consider that many viruses are incredibly simple.
­­When you listen to the news, you hear about many different forms of electronic infection. The most common are:

• Viruses - A virus is a small piece of software that piggybacks on real programs. For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce (by attaching to other programs) or wreak havoc.
• E-mail viruses - An e-mail virus travels as an attachment to e-mail messages, and usually replicates itself by automatically mailing itself to dozens of people in the victim's e-mail address book. Some e-mail viruses don't even require a double-click -- they launch when you view the infected message in the preview pane of your e-mail software [source: Johnson].
• Trojan horses - A Trojan horse is simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk). Trojan horses have no way to replicate automatically.
• Worms - A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well.

­In this article, we will discuss viruses -- both "traditional" viruses and e-mail viruses -- so that you can learn how they work and understand how to protect yourself. (from : http://www.howstuffworks.com)