Kiosk systems auto-upgraded??

[whitetr6]

I have 10 systems that were happily running 10.04 with a Gnome desktop and a video slideshow autostarting on reboot. Until this morning. They all just popped up a screen saying Welcome to Ubuntu 11.04 Natty Narwhal.

What did I do or not do to cause that to happen? I have updates set manually on these machines, or so I thought since I have always had to run my updates manually in the past.

Please explain so I can prevent this from happening again.

Thanks

[whitetr6]

Never mind. The information from the users at the remote site was inaccurate. There was a pop-up on screen, but no upgrade had taken place.
Thanks