Just so we're straight on terms: a botnet is a network of infected computers remotely controlled by an operator to do things their owners don't know about. Stuff like sending spam, for instance. It's very possible your computer is part of a botnet.
Rustock is one of the largest and spammiest botnets in the world and it was "flatlined" this week, rendered inoperable as a result of a massive attack by spam fighters on Wednesday. As a result, the amount of spam circulating online took a nosedive. Rustock has been hit before and rallied back, as have many botnets, since the computers are still infected. Security expert Bryan Krebs compares these computers to sheep without a shepherd. But for now, the network of spam-fighting crusader/hobbyists is celebrating a huge victory.
From Krebs on Security:
Spam data compiled by the Composite Spam Blocklist, the entity that monitors global junk e-mail volumes for the anti-spam outfit Spamhaus.org, shows that at around 2:45 p.m. GMT (10:45 a.m. EDT) spam sent via the Rustock botnet virtually disappeared. The CBL estimates that at least 815,000 Windows computers are currently infected with Rustock, although that number is more than likely a conservative estimate.
Of course, if you really wanted to get offers for Viagra from Russia, today is a bleak day.