A map of Waledac infections (Microsoft graphic)

In an operation worthy of a spy novel, Microsoft says it has disrupted a botnet known as Waledac that's believed to have infected hundreds of thousands of computers. The company says the botnet was able to send more than 1.5 billion pieces of spam every day -- until the company secured a court order allowing it to secretly cut the spammers off from the network before they realized what hit them.

The initiative, known internally as "b49" is described in detail today in a Wall Street Journal piece and a Microsoft blog post. A botnet is a network of PCs that have been infected with malicious code that allows them to be controlled remotely, often without the user's knowledge.

"Three days into the effort, Operation b49 has effectively shut down connections to the vast majority of Waledac-infected computers, and our goal is to make that disruption permanent," the company says in the blog post. "But the operation hasn’t cleaned the infected computers and is not a silver bullet for undoing all the damage we believe Waledac has caused. Although the zombies are now largely out of the bot-herders’ control, they are still infected with the original malware."

The company is directing Windows users to its Protect Your PC site and Malicious Software Removal Tool.