A free security tool is slaughtering the Zbot botnet, having cleaned the malware responsible for harvesting zombie computers from almost 280,000 machines. Last week, a new version of the Malicious Software Removal Tool was released, updated to tackle Zbot, the 14th largest botnet worldwide. In just a few days, MSRT has delivered a heavy blow to the network of zombie computers, with a few hundred thousand PCs having been cleaned. MSRT was refreshed and offered to all Windows users via Windows Update on October 12, as a part of the company’s monthly release of security bulletins. “Since the release of MSRT on Tuesday we have removed Zbot 281,491 times from 274,873 computers and is the #1 family of malware removed (which is not uncommon the month a family is added),” revealed Microsoft’s Jeff Williams. “Of the 1,344,669 computers cleaned, this is about 1 in 5, a ratio that’s higher than we typically see even when accounting for the normal, first-month spike which results from adding a new family but not exceptionally so.” The tackling of Zbot is just the latest move from Microsoft in the ongoing war the software giant is waging against botnets worldwide. “To put this in greater perspective the removals of Zbot are almost as many as the removals of the #2 and #3 malware families this month combined (Win32/Vundo and Win32/Bubnix respectively),” Williams added.