Got a difficult infection on your computer? Microsoft Safety Scanner may be your answer. It is a free tool available for download from the Microsoft website. The tool is intended to be an aid to already installed anti-virus software on your computer that works alongside other Microsoft software such as Internet Explorer and Windows Live to create a suite of protection.
The downloaded software only lasts for 10 days. Why? That is a good question. It seems that Microsoft Safety Scanner is intended to be a quick fix for a particularly hard-to-remove infection. It seems to work well for removing fake security software that is laden with hidden malware. This type of hoaxware is extremely hard to remove with normal security software.
http://www.microsoft.com/security/portal/mmpc/help/mss.aspx