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I have been infected by rootkit.win32.agent.biiu.

I boot up with 'Last Known Good Configuration' and do a full scan with Kaspersky. It catches many c:\windows\drivers\?.sys and either deleted or quarantined them.

How can I restore the original/correct .sys file? Boot with safe mode after full scan perhaps?

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up vote 4 down vote accepted

Chances are that those .sys files were just viruses, and not legitimate files. None the less, it wouldn't be a bad idea to click start, run, and type this:

sfc /scannow

It will prompt you for your Windows CD and repair any files that have recently been replaced. Be sure to re-run Windows Update after doing this.

You can find more information on this command at

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This is so useful, thanks! After sfc scan, it didn't found any thing wrong. However, I have a question for those virus .sys files. Since they are not necessary for WinXP at all, how do they get loaded or executed? Does WinXP load everything in drivers folder? Thanks. – Stan Sep 15 '10 at 7:45
@Stan - the viruses place themselves in that location and arrange for themselves to be triggered (Window's shouldn't run them by default, but they'll just add themselves to the relevant lists). They do this so that people don't notice (for example, in Task Manager) and/or are scared to touch them (because they are "system" files) - it's a psycological trick against the user to reduce the chance of detection and removal. – DMA57361 Sep 15 '10 at 7:53

You could restore to a system restore point if they were confirgured to save and you have a save point that's before the virus infection, but not too old as to be painful.

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the .sys files are compressed in the Windows CD so i dont think it can be extracted, but how about installing winxp on a virtual machine and then copy and paste the .sys files from there?

i dont think that u lost all the system files - just some files that were infected - so its not risky to replace them

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You can definitely get files of the Windows disc. Easiest method is to run sfc. – Brad Sep 15 '10 at 13:27

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