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Happy birthday, Brain.A

Twenty years ago this month the first PC virus was discovered. It's extinct now, but its kin continues to pester computer users.

Unless you're in the antivirus business, it's probably not worth celebrating. But 20 years ago this month, the first PC virus was discovered.

Dubbed Brain.A, the virus got onto computers via floppy disk and infected the boot sector of PCs, according to Finnish antivirus maker F-Secure, which devoted a blog post and news release to the occasion on Thursday.

"While the virus 'Brain' itself was relatively harmless, it set in motion a long chain of events leading up to today's virus situation," F-Secure said.

Brain.A and other "boot sector" viruses are long extinct. The same could be said of the medium used to spread them: The boot sector is typically the first 512 bytes of a hard disk or floppy disk.

Viruses have evolved significantly since Brain.A, but boot sector viruses were around from 1986 to 1995, according to F-Secure. Macro viruses arrived next, exploiting early Microsoft Windows operating systems. The advent of e-mail subsequently propelled e-mail viruses such as the I Love You and the Anna Kournikova virus.

The first worm surfaced two years after Brain.A, when the Morris Worm hit Unix systems connected to the Internet.

Viruses have caused significant pain for computer users. The FBI on Thursday said computer crime cost U.S. businesses $67.2 billion over a 12-month period, with viruses and worms the biggest culprits.

"Certainly the most significant change has been the evolution of virus-writing hobbyists into criminally operated gangs bent on financial gain," Mikko Hypponen, chief research officer at F-Secure, said in a statement. "And this trend is showing no signs of stopping." There are currently more than 150,000 known viruses and the number continues to grow, according to F-Secure.

At the same time, revenue associated with antivirus products reached $3.7 billion in 2004, increasing 36 percent from 2003 to 2004, according to IDC. The research firm forecasts the antivirus market will increase to $7.3 billion in 2009.