The legacy of a botnet once responsible for half of the world's spam is almost finished Microsoft says.
An industry initiative led by Microsoft this year had cleaned more than 50 percent of computers infected with and previously under control by the prolific Rustock botnet.
According to the "Battling the Rustock Threat" report more than 700,000 IP addresses were infected with Rustock as of 18 June last year, down from more than 1.6 million on 26 March.
"That's great news, and the infection reduction has happened much more quickly than it did for [the Waledac botnet] over a similar period of time last year, but we still have a long way to go," Microsoft senior attorney Richard Boscovich said.
Infections in India, Russia and the Ukraine had each dropped by a whopping 70 per cent.
India had the highest initial infection rate and continued to house almost 100,000 compromised machines. The United States ranks second with more than 55,000 infected computers.
The Rustock botnet controlled a network of more than a million computers at its hieght and used them to pumped out some 40 billion spam emails per day. It sold everything from software to discounted drugs like Viagra and Cialis, and counterfeit goods.
The takedown, dubbed Operation b107, involved Microsoft, law enforcement, industry and academic partners.
The operation severed the connection between Rustock's command-and-control servers, which sent out instructions to infected computers.