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But none of these antiviral programs are foolproof. Virus writers are constantly making end runs around the barricades erected against them. Even a total purge of a computer system is no guarantee against reinfection. McAfee reports that 3 out of 4 of the installations he visits suffer a relapse within a week, usually from disks missed on the first go-round or carried in from the outside. In recent months, a pesky new type of virus has emerged. So-called retroviruses are designed to reappear in systems after their memories have been wiped clean. Other viruses infect a computer's hardware, speeding up a disk drive, for example, so that it soon wears itself out. Particularly dangerous are bogus antiviral programs that are actually viruses in disguise and spread infection rather than stop it.
Where will it end? The computer world hopes that the novelty of software viruses will pass, going the way of letter bombs and poisoned Tylenol. But even if the epidemic eventually eases, the threat will remain. The uninhibited program swapping that made the early days of the computer revolution so exciting may be gone forever. Never again will computer buffs be able to accept a disk or plug into a network without being suspicious -- and cautious.