I keep my PC (running XP Pro & latest patches) up to date, run a software firewall (and an SPI firewall in my router), spybot s&d, adaware & up to date virus scanner.
I was using my PC this morning (no the one I'm on at the moment) and received several updates whilst I was browsing a photography forum. I didn't accept the "restart now" option because I would do that at a later time. After I had finished I rebooted the PC and found that I couldn't enter my password - the keyboard didn't register any keystrokes (although you could toggle the "numlock" LED). I rebooted again only to find that the same thing happened and it was then that I noticed that I didn't have a mouse pointer. Moving the mouse revealed that the pointer was at the bottom left of the screen and wouldn't move away from there!
I rebooted into safe mode - my keyboard worked but the mouse was still at the bottom left of the screen. I "rolled back" to a prior point in time and when the PC rebooted I still had the same problem.
There seems to be some strange things happening lately! My son has had problems with his PC and a work colleague also.