Microsoft's anti-virus clean-up tool has removed 16m instances from 5.7m Windows PCs during its first 15 months of operation. Windows Malicious Software Removal Tool (MSRT), the malware removal software which Microsoft releases free of charge and updates every patch Tuesday, has been executed 2.7bn times on 270m computers since its debut in January 2005. Stats from its use present a new perspective on how bad the Windows malware problem really is.
On average, the tool removes at least one instance of malware from every 311 computers it runs on. It has removed at least one backdoor Trojan (the most damaging types of malware, which give hackers control of compromised PCs) from around 3.5m unique computers. Zombie bots represent the most common flavour of backdoor code encountered by Microsoft's tool.
Rootkits, forms of malware that hide their presence on infected PCs, are also a growing threat. Of the 5.7m unique computers disinfected by Microsoft's tool, a rootkit was found in 14 per cent of cases. But this figure drops to 8 per cent if the "WinNT/F4IRootkit", the rootkit distributed on some Sony music CDs, is excluded. In one of five cases at least one Trojan was found on PCs also contaminated by a rootkit infection.
"The malware problem appears to be migratory in nature. Most of the computers cleaned with each release of the MSRT are computers from which the tool has never removed malware," Microsoft's researchers conclude. A white paper from Redmond's anti-malware team on their experience with their anti-virus clean-up tool can be found here. ®