A hoax is a message or warning that is not true. Computer virus hoaxes can cause a lot of confusion and wasted time amoung ordinary computer users, and sometimes quite technical people. Computer virus hoaxes are quite common and they usually warn about a new computer virus that no anti-virus software detects and which can do a lot of damage to files or computers. The biggest give-away is that they ask people to pass on the warning to everyone they know - this is how the hoax spreads.
In general, ordinary users should NEVER pass on warnings, and you should only expect to get warnings from a trusted source: your company's data security officer, or your ISP's technical support. The information in a real warning will be verifiable: if it says the information was released by Microsoft, there will be a link or reference to a Microsoft web page or press release.
If you receive a warning that you do not know whether to believe, contact your data security office, helpdesk, or us to check - we would rather answer your question once than questions from the hundreds or thousands of panicing people you might pass the message on to.
The links below have descriptions of many common hoaxes.