OT:surprise Bomb in OS X…?

[John H. Lincoln]

I've never seen a crash like this before:

I was peacefully minding my own business, (on my Cube/Studio display 
set-up: 1.25 GB RAM, 80GB HD, GeForce2 card) –– running a half-dozen 
apps under OS X (v.10.2.4), when suddenly… a translucent grey curtain 
descended from the top of the display, halting all computing functions.

And in the center of the screen, on a white background, the message: 
"You need to restart your computer. Hold down the power button for 
several seconds or press the Restart button."

This message was repeated in French, German, and Japanese. And at the 
bottom, a few code numbers, including my IP number.

OK, I had to re-boot. Any ideas what this was, or where it came from?

Anybody seen this before? TIA.
============================
John H. Lincoln
Digital Media Designer
Mallorca, Spain