Prior to the take-down, Rustock was capable of sending as many as 30 million spam messages daily.

"Cleaning the users' PCs is an important part, but really this shows that a technical countermeasure along with a legal countermeasure works," said Boscovich, talking about the two-pronged approach of seizing servers and shutting down Rustock's backup communications.

And the impact goes beyond Rustock.

"The minute you take down Rustock, what does that do to those who want to send spam?" Boscovich asked. "They have to find other botnets. But if you're a botnet herder, and you just saw Rustock go down -- with years of work coding and planting malware and maintaining the botnet -- you're going to charge more. And that's an impact on spammers' cost analysis, as it becomes more and more expensive to send out spam."

Statistics from Symantec seemed to prove Microsoft was on to something.