Thanks for your help.
I have followed your instructions but don't have an lvsrev.exe file appearing either in HijackThis or C:\WINDOWS\System32. I don't have an InvisibleDrvNT.sys file in the drivers folder either.
I do however have a xx_lvsrev.exe file in the System32 folder.
There are also xx_apigrab.dll and xx_wartsvr.exe
Shall I get rid of some/all of these?