By Adam Lashinsky

(FORTUNE Magazine) – San Francisco Founded 1998

In the cloak-and-dagger world of spammers, tricks for sneaking through omnipresent filters are commonly used. But one company, Brightmail, has shown that it can use the same tricks to stop the spam. The company operates some two million decoy e-mail addresses that it uses to attract the bad guys. Once Brightmail's so-called Probe Network lures a spammer into its web, it then transmits kill-that-address information to its customers, companies like Microsoft's MSN and Internet service provider Earthlink. The updates come fast and furious, roughly every ten minutes. Brightmail says it processed 93 billion messages in March alone.

As the pesky spam problem has multiplied, so too have Brightmail's revenues, jumping from $2 million in 2000 to $26 million last year. The profitable firm is expected to go public this year, meaning a big payday for VCs Accel Partners, Technology Crossover Ventures, and founder Sunil Paul, 39, an early product manager at America Online. --Adam Lashinsky