What makes an ECU go bad?

["Horch, August" <Horch.August@tci.com>]

Came home to further troubleshoot the cut-out on the TQ, and according
to the Good Book of Bentley the Control Unit is shot.  OK, so what makes
an ECU go bad?  The problem first showed it's head after it was parked
outside a theatre long enough to watch a movie.  Not a terribly long
time.  The cutout has gotten progressively worse, to the point where I'd
rather be driving the Explorer to work.  Sad, I know.  Ideas?

-August