At some point, all of us have received a "helpful" message from a co-worker or family member warning us about the latest internet virus. Unfortunately, the overwhelming majority of these messages are hoaxes - scare alerts started by malicious people and then passed on by well-intentioned users who think they are helping by spreading the warning. The message itself is the virus, and it depends on your goodwill (and gullibility) to spread.
Do not forward hoax messages. Some hoax messages carry malicious instructions about how to delete certain "corrupt" files - files that actually are not only safe but even necessary to your computer. In others, the hacker offers a convenient link or tool to "check your computer and remove the virus" or "improve your performance". Instead of downloading an anti-virus tool, you're actually loading the malicious software itself.
Even "innocent" messages with no direct malware attached have caused the e-mail systems at some companies to collapse when hundreds of users forwarded a false alert to everybody in their address book.
If you receive an alarm email about a virus from anyone except your own IT department, just delete it, especially if the message includes any "special" instructions. (The instruction to run your own anti-virus program is probably safe but I'd never trust someone else to tell me to load a piece of software.)
If you suspect that the message might be legitimate, forward it to your IT department and let them determine if a wider announcement is appropriate. You can also check at f-secure.com for a good list of known virus alarm hoaxes.