ntoskrnl.exe infected with Trojan.Dropper

Hi

 

A large amount of obscene websites appeared on our internet browsing history today. I did a scan with Norton 360 and no issues arose, however I did a scan with this free download version of Spyhunter3 and it found a Trojan.Dropper virus in the ntoskrnl.exe. How do I fix?

 

The file path that it identified is C:\WINDOWS\$hf_mig$\KB890859/SP2QFE/ntoskrnl.exe

(also there are no viruses showing in my registry at all - just this one file)

 

I looked on the Symantec website against Dropper.Trojan Virus and it says to delete the infected files (after following all of the other steps of course), however the computer needs this ntoskrnl.exe doesn't it? If I delete that, wont that cause problems?

 

 I also noticed there was a Latest Rapid Release Version (revision 035) of this virus dated 20/7/2009. If you can please help that would hugely appreciated. Thanks.