Actually, Nemesis indicated that restoring a drive image from a previous date corrected the problem, so it must have been a software cause. It's impossible, of course, to say what specifically would have caused it but I'd suspect that it would have been malware of some variety, and most likely one which included a 'keylogger' component. Improve the internet security software installed on the system would be my advice.
DMR, you need to practice up on your Windozing skills, I suspect. I've not had to use a '3-fingered salute' for ages! :p Or perhaps I could be excused for suggesting you need this keyboard?