Virus blocking the installation of antivirus
It sounds like conficker , Downadup (or Conficker) is a network worm that takes advantage of vulnerabilities in Windows to spread. Its removal is complicated by the fact that it blocks many known antivirus software and associated websites.
BitDefender Labs has detected a new and more aggressive Downadup version. It spreads using a Windows RPC Server Service vulnerability and is called Win32.Worm.Downadup.Gen.
The new version is more resilient to disinfection. Once the system is compromised, the worm disables Windows Update and blocks access to most of the anti-virus websites in order to hinder the user to disinfect his machine.
BitDefender is the first to offer a free tool which disinfects all versions of Downadup. This domain is the first to serve a removal tool without being blocked by the e-threat.
download from here http://www.bdtools.net/download/dcleaner.zip
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Try a online virus scan, or install and scan during safe mode.
some online Scanners
http://www.pandasoftware.com/products/activescan.htm
http://us.mcafee.com/root/mfs/default.asp?cid=9913
http://housecall.trendmicro.com/
