Trojan.Webkit!html infection. Help please

System: Windows 7 Home Premium

HP G6 laptop x64 based

Backup job using the standard Win7 utility (backing up users files from C:\ to a USB drive)l started failing yesterday reporting errors whist trying to read from the volume shadow copy.

Looking at the NIS log I discover that my PC appears to be infected with the Trojan.Webkit.html as several entries have started to appear in the “resolved” threats log – detected by Auto Protect. But it can’t be resolved as the entries keep appearing at random intervals. Example from NIS log:

Trojan.Webkit!html

 Removed

No action required

Device\harddiskvolumeshadowcopy13\users\MY USER ACCOUNT NAME\appdata\local\mozila\firefox\profiles\6fxm5klf\cache\a\a6\7ed83d01

No fix attempted

 

I ran a full system scan using Malwarebytes and it reported no threats. I then ran a NIS full system scan in Safe Mode and again nothing was reported apart from a couple of tracking cookies.

I’ve not attempted anything further as I’m not competent enough without help. 

Can anybody help fix this? 

I have a USB stick.

Regards

Newboy