Although, I think it is a false positive, here is what the Sophos Virus Removal Tool
2013-05-17 07:26:22 Component rkdisk.dll version 1.5.30.0
2013-05-17 07:26:22 Version info: Product version 2.3
2013-05-17 07:26:22 Version info: Detection engine 3.43.0
2013-05-17 07:26:22 Version info: Detection data 4.89G
2013-05-17 07:26:22 Version info: Build date 5/8/2013
2013-05-17 07:26:22 Version info: Data files added 292
2013-05-17 07:26:22 Version info: Last successful update 5/17/2013 7:26:18 AM
>>> Virus 'Mal/Behav-035' found in file D:\Download\Tweaking.com - Utils\svchost.exe Lookup Tool v1.5.0\Tweaking.com - svchost.exe Lookup Tool\lookup_svchost.exe
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Mal/Behav-035 is a file that displays characteristics or behavior found exclusively within malware.
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www.sophos.com/en-us/threat-center/threat-analyses/viruses-and-spyware/Mal~Behav-035/detailed-analysis.aspx=========================================================
Regards,