Vista unexpected restart

While working on my taxes, with Turbotax, Quicken, and 2 Excel spreadsheets open, Vista briefly (about one second) presented a message over each running window and closed each window (without asking permission), then presented a message something like "updating configuration files" then shutdown and restarted.

Sorry I can't be specific, as I was in shock from watching my extensive work in the two spreadsheets disappear. Sure enough, when I restarted the spreadsheets all my work in this session was gone.

I am a very experienced computer user, and have seen lots of hardware and software failures in my time. This one, however, looks like a really bad failure in Vista automatic updates design. I must say I am very upset at the loss of over 2 hours work. Do I have to go back to the early days habits and save my spreadsheets every 5 minutes or so?

This is a powerful (Intel MB, core 2 QX6700, 2GB Ram) new system, latest bios update, with a clean install of Vista ultimate, with all updates applied. Also running Office XP, with all updates applied. Norton Internet security (vista support version) sees nothing wrong. Any idea what might have happened?