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Holiday greetings from friends and family are quite common at this time of year but, before you eagerly open that attachment, make sure it's not the Klez virus pretending to be from your favorite relative or chum. Klez, the most prevalent virus of 2002, was engineered to change its message around certain occasions to masquerade as a greeting card. Thus, that message from your dear Aunt Emily with the subject "Happy Fun Christmas", is most likely the Klez virus. Of course, this doesn't mean your Aunt Emily is necessarily infected with Klez - the virus spoofs the From address so only a view of the headers will divulge the true sender.

If your mail client has not been configured for proper protection, the choice of whether to open the attachment may be taken out of your hands. Klez takes advantage of a security vulnerability that allows the attachment to be automatically executed just upon reading or previewing the email message. Of course, there are many types of vulnerabilities - particularly in Microsoft products - that leave your system vulnerable to harm. Make it your New Year's Resolution to routinely check the Windows Update site to ensure your system is patched against these exploits.

The Klez holiday greeting doesn't confine itself to just Christmas. The Klez worm creates seasonal greetings for Halloween, New Year's, Valentine's Day and April Fools' Day, among others. Indeed, between Klez and the Friend Greetings scampaign, legitimate greetings cards may end up being viewed with suspicion and deleted unread.