Computer viruses have struck some area businesses.

"This is the first time I've been infected, and it scared the hell out of me," said Wayne Johnson, chief executive office of Thunderbird Software.The "stoned" virus and a version of the "Jerusalem" virus are causing havoc with his computers and have turned up in computers of at least two of his clients.

"I feel like a doctor who's got a real serious disease and is trying to check all his patients," he said.

Computer viruses are programs their creators attach to other programs, often legitimate applications. When the legitimate program is executed, the virus program attaches itself to other programs. Eventually the virus program usually does some damage, such is deleting all the files.

The destruction often is accompanied by a "gotcha" type message, such as the stoned virus' "Your PC (personal computer) is now stoned!"

Common guards are to maintain backup copies of programs and data and check systems periodically and all new programs for known viruses.

John McAfee, Santa Clara, Calif., chairman of the Computer Virus Industry Association and developer of some of the most popular programs for detecting and treating viruses, said the two strains first invaded Utah and most other parts of the nation at least two years ago.

Computer owners in Provo and Salt Lake City have reported dozens of stoned and Jerusalem virus infections during the past two years, he said.

McAfee Associates receives about 100 infection reports weekly from around the world. The stoned virus originated three years ago in New Zealand, and the Jerusalem strain also is about 3 years old and was traced to Hebrew University in Jerusalem.

"Those two are the most common viruses anywhere in the United States," McAfee said. "The two of them account for almost 90 percent of infection reports."