From TechWeb:
Backdoor Trojans are a clear and present danger to Windows machines, Microsoft said Monday as it released the first-ever analysis of data collected by the 15-month run of its Malicious Software Removal Tool, a utility that seeks out and destroys over five-dozen malware families.
According to Microsoft’s anti-malware engineering team, Trojans that, once installed, give an attacker access and control of a PC, are a “significant and tangible threat to Windows users.”
Of the 5.7 million unique PCs from which the Malicious Software Removal Tool (MSRT) has deleted malware, 3.5 million of them — 62 percent — had at least one backdoor Trojan.