Microsoft has cleaned almost 1 million computers from infections involving password stealing malicious code in just a single week. The Redmond company's Malicious Software Removal Tool managed to remove malware harvesting for accounts/passwords and even credit card information from no less than 860,000 PCs. According to the software giant, in the Password Stealers and Monitoring Software category, MSRT tackled the following malware: Win32/Frethog with 95,581 compromised machines, Win32/Bancos with 92,565 infections Win32/Lolyda, detected on 54,871 computers. There are also two worms, Win32/Taterf with 347,424 detections and Win32/Koobface removed from 78,113 infected machines.

“Three of the top 10 [threat families] are password stealer threats. In fact there are five if you count those two worms, Taterf and Koobface, both of which have critical payload of stealing user data. Or consider six – Alureon trojan goes for users’ password and credit information as well. Adding them together there are 859,842 machines infected by password stealer threats when we are only talking about the top 10 threats. Note this is not a direct sum since some machines were infected by more than one of these threats,” revealed Scott Wu, program manager at Microsoft.

The Redmond company underlined the fact that malicious code designed to distribute rogue antivirus programs continued to rank high among widespread malware families. It is the case of Renos, a Trojan horse downloader that serves as a distribution channel for fake security solutions. Renos was detected and removed from 78,113 computers.

“Out of the top 10 threat families six moved higher in ranking compared to last month. Some of these six threat families like Alureon and Vundo have been around for more than two years while other like Koobface have only been seen in the ecosystem for several months. This indicates each threat has its own lifecycle and it appears that sometimes malware authors are willing to reinvest in their existing distributions instead of moving to somewhere else,” Scott Wu added.

The Malicious Software Removal Tool is available for download here.