Microsoft has begun the process of attempting to wipe out the notorious Waledac spam botnet.
Waledac is one of the largest botnets in the US, estimated to have comprised hundreds of thousands of computers to send over 1.5 billion spam messages a day.
Microsoft said that over 18 days in December last year, 651 million spam emails linked to Waledac were delivered to Hotmail accounts alone.
The botnet takedown began earlier this week under an initiative called Operation b49, and has had a quick effect, according to the software giant.
"Microsoft does not accept the idea that botnets are a fact of life. We are a founding member of the Botnet Task Force, a public-private partnership to join industry and government in the fight against bots," said Tim Cranton, associate general counsel at Microsoft, in a blog post.
"That's why I'm proud to announce that, through legal action and technical co-operation with industry partners, we have executed a major botnet takedown of Waledac, a large and well-known spambot."
The action is the result of a court decision granting Microsoft the right to cut off 277 internet domains believed to be run by criminals associated with Waledac.
However, the work is not over and Microsoft urged internet users to protect themselves, or risk being enablers for cyber criminals.
"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," said Cranton.
"But the operation has not 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. To help make sure you are not infected by this or other botnets, our advice is to follow Microsoft's Online Safety guidance."
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