Blue Security was an Israeli company that fought spam with spam:

Eran Reshef had an idea in the battle against spam e-mail that seemed to be working: he fought spam with spam. Today, he’ll give up the fight.

Reshef’s Silicon Valley company, Blue Security Inc., simply asked the spammers to stop sending junk e-mail to his clients. But because those sort of requests tend to be ignored, Blue Security took them to a new level: it bombarded the spammers with requests from all 522,000 of its customers at the same time.

That led to a flood of Internet traffic so heavy that it disrupted the spammers’ ability to send e-mails to other victims — a crippling effect that caused a handful of known spammers to comply with the requests.

Then, earlier this month, a Russia-based spammer counterattacked, Reshef said. Using tens of thousands of hijacked computers, the spammer flooded Blue Security with so much Internet traffic that it blocked legitimate visitors from going to Bluesecurity.com, as well as to other Web sites. The spammer also sent another message: Cease operations or Blue Security customers will soon find themselves targeted with virus-filled attacks.