Most sinkholing efforts divert all traffic from a malicious domain, blocking access for everyone.

Redwood City, Calif.-based Nominum provided technical assistance and its DNS software to the operation, which Microsoft has dubbed "b70."

"This was a surgical strike," said Craig Sprosts, Nominum's general manager for fixed broadband solutions, in an interview today. "Microsoft took ownership of the [3322.org] domain and basically created a more surgical access to the good domains and blocked the bad."

The problem posed by the sinkholing of 3322.org, with its millions of subdomains, was technically difficult, said Sprosts and a college, Daniel Blasingame, general manager for embedded solutions at Nominum.

"Microsoft needs to be able to change the list of the good and bad subdomains on the fly," said Blasingame, who cited that as well as the sheer scale of the project as factors complicating the operation.