Unfortunately, it's no longer a matter of "if" someone will send you a virus, but "when". These recommendations will limit the likelihood of getting infected by a computer worm or virus.

1. Get Antiviral software. We recommend two products. Norton Anti virus and AVG Anti virus, a free anti virus tool for US users. We primarily recommend Norton Anti virus No reason other than we like it's look and interface a little better and Symantec is a trusted company that we don't expect to go anywhere anytime soon (that's not always the case with free versions). NAV has an automatic update feature and if you have ever had anything wiped out by a virus, you realize it's worth your time to buy some software to prevent it. Purchase online or see their download section for a free Trial.
Web site: http://www.symantec.com Note: When purchasing their anti virus product they also give you options to "upgrade" to their System Works or other Security Products. There is no need to do this. Save your money. Free anti virus Software
Speaking of saving money and despite my comments above about free anti virus software, we have found this FREE Anti virus product from GriSoft to be just as good as any of the paid programs.
Download it here: http://www.grisoft.com

2. Patch your System/Software Most viruses and worms on the loose today are taking advantage of well publicized" holes" in your email or operating system software. Keep your system "patched" and you'll be immune to many of the most popular viruses. Start here: http://windowsupdate.microsoft.com
From that screen click on product updates. Download all critical and security updates. Also download any in the recommended section that look like they may apply to you. This should help your system stability (fewer crashes and lock-ups) as well as security. Don't open attachments!
The vast majority of viruses are executed by opening an attachment. This applies to friends as well as strangers. Unless you know this person has sent you the attachment sitting in your inbox, don't open it. A "no attachment" policy is a good recommendation for any business. Very often infected people send you viruses with attractive subjects like "what do you think of this?" and have no idea their computer is sending out email on their behalf. Scan everything:
If you know what the attachment is, and are expecting it, then before you open it, save it to your hard drive and scan it, just to be sure the sender does not have a virus that is infecting other documents.
Please note: The info here is provided as a public service in good faith. We can not be responsible for any damages that may occur while attempting to clean your system.