Updated MWB this morning to DB v4298 and started usual weekly Quick scan. After 2m31s, the program stopped at file c:\program files\mozilla firefox\plugins\npsabffx.dll. Could not pause/stop/or exit the program, PC was locked up, and I had to do a reboot. Ran MWB again, but same time, same file and same lock up once more. I have learned that this particular file is installed by SuperAdBlocker and has been in my FF plugins for some considerable time. After reading advice from Mozilla, I renamed this file, and ran MWB again, this time successfully. Is there any explanation why this file should be causing a problem? I can think of nothing which has changed on my PC since the previous scan a week ago, other than the updated MWB database. Should confess that I always run MWB in normal XP SP2 operating mode, rather than safe mode, but have never yet been affected by malware.