We have liftoff! I am clean at last!
What I did was:-
1. Delete crashlog.tar.gz from my System32 folder but leave it in the Recycle Bin just in case.
2. I then disabled System Restore correctly - Start-Control Panel-click on System and check the Disable System REstore box. REstart computer and check that crashlog.tar.gz was not in my System folder - no it wasn't.
3. Disable my screensaver.
4. I started a scan and it didn't pick up any infected unp files but it picked up the crashlog.tar.gz file in the Recycle Bin. I stopped the scan, emptied out the Recycle Bin (it was teh only file in it anyway, I emptied it yesterday!)
5. Avast picked up more infected unp files on the next scan, so I stopped the scan and deleted them from the Temp/_Avast4_ folder and emptied the Recycle Bin. I double checked System32 again but the file crashlog.tar.gz was not in it thank goodness.
6. I ran a full clean scan.
7. I restarted the computer and ran another full clean scan (I did go online again adn double checked your posting above, and Avast downloaded some updates whilst I was doing it - so the scans were absolutely up to date).
Tomorrow I plan to redo that backup - it's needed urgently now - and I will destroy those disks I burned today.
I am pretty certain now that the virus is gone and would like to thank you very much indeed for all your kindness and help over the last few days. I don't know where I'd have been without all your patience, advice and help.
I do a lot of computer graphics and have my own web site so if I can do anything for you in that line please contact me and I'll be glad to help.
Avast were recommended to me by the principal of the web school where I study, Richard Dean of
http://vu.org. I have yet to find him wrong on software of any kind!