(FORTUNE Magazine) – Computer viruses, those digital scourges, are infecting America's PCs faster than chicken pox moves through a kindergarten. The number of known computer viruses trebled to about 6,000 over the past 12 months. But fears of massive terminal terror have not materialized because the virus police are on the case, and most of the bad bugs are now locked up in security labs. At last count, there were 180 viruses actually out there, but most are graffiti-like and flash brainless phrases such as GUNS AND ROSES RULE! on your screen.

Certainly viruses can be a pain in the Pentium. Micki Krause, program manager of information security at Rockwell, says her company is attacked about a dozen times each month. "It's frustrating, annoying, and expensive," she says. One virus nailed nine Rockwell file servers and 630 PCs in 30 global cities. It took the company a month to kill the intruder, at a cost of about $44,000.

Eastern Europe, particularly Bulgaria, is the leading exporter of viruses. Bulgaria? This nation is rich in computer scientists, but not, alas, employment. So computer jocks take any job to support themselves and write viruses to keep their programming juices flowing. Virus writing is catching. Antiheroes like the Dark Avenger (a Bulgarian) and Slash Woo (Chinese) teach disciples the arcane code that conjures demons like Monkey B and Nymphomaniac Mitosis.

Battling these forces are virus-busters like the eight-person team at Symantec, operating out of a stealth lab replete with a skull and crossbones on the door. Disks--the primary carriers of viral infection--are allowed in but never out. The team examines, then zaps, about 30 viruses a month.

So viruses are a headache for computer security pros, but what about home machines? Microsoft says not to worry. It won't be bundling antivirus software onto its new Windows 95 operating system. "It's really a corporate product and not so important for individuals," says Russ Stockdale, Microsoft's group manager of personal systems.

Don't tell that to Symantec, whose Norton antivirus program ($129) is a top seller. Many PC users consider such programs a cheap form of insurance. Of course, if sales slowed, the company could always release some of those critters it has locked up. - Andrew E. Serwer