"W97M/Prilissa" - a virus set to go off on Christmas Day - struck 10 Fortune 500 firms on three continents last week.
Prilissa is based on two better known bugs, the Melissa worm and the PRI virus. The new virus affects machines running Windows 95 or 98, and Word 97.
Like Melissa, Prilissa comes as an e-mail attachment which, if opened, will send itself to the first 50 names in a user's Outlook or Outlook Express e-mail address book.
Once activated, Prilissa creates a Microsoft Outlook e-mail message with the subject line "Message From (Office 97 user name)" and a message body that says "This document is very Important and you've GOT to read this!!!"
If the date is December 25, the virus unleashes a destructive payload to overwrite the existing C:/AUTOEXEC.BAT file with instructions to format the C drive - and the user discovers a nasty Christmas surprise: the deletion of all data on their hard disk.
Most anti-virus vendors are posting definition updates and fixes for the virus. A complete report is online at www.zdnn.com .