The worm comes disguised in e-mail. It arrives with a friendly message: "Hi! I received your e-mail and I shall send you a reply ASAP. Till then, take a look at the attached zipped docs."
If the user opens the attachment, the trojan horse is activated. The worm hunts through your hard drive, wiping out documents, spreadsheets and other files.
The bug also contaminates Microsoft Outlook, Outlook Express, Exchange and other mail programs and sends automatic e-mail replies that infects other computers.
Microsoft was hit and closed down its e-mail system. Companies with large computer networks are particularly vulnerable.
Fixes for Worm ExploreZip are already available on the Web sites of all anti-virus scanning software vendors.
A member of the Computer Emergency Response Team at Carnegie Mellon University says the best prevention is to "be a little paranoid." With more computers networked, viruses, worms and trojan horses will become more common.
Individuals and small business owners should download or buy anti-virus scanning software and do daily online updates to protect themselves. Andalwaysthink twice before opening attachments to suspicious e-mail.
ExploreZip only affects PCs running Windows 95, 98 and NT. Macintosh and Unix systems are not affected.