With all the fuss over the Michelangelo computer virus, PC users may be overlooking another threat to their data: a bug that's set to chomp their files on Friday, Mar. 13.

Unlike the Michelangelo bug, the so-called Jerusalem virus is designed to destroy only certain files on an infected PC's hard drive. And it's widespread: A recent survey by market researcher Dataquest found that 37% of companies with bugs in their networks reported finding a Jerusalem strain. While that's bad news for system managers, it's a delight for makers of antiviral software. XTree, of San Luis Obispo, Calif., says its 24-hour order phone hasn't stopped ringing.

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