Regarding securelevel startup window

Hi All,

I've been re-reading Design and Implementation cover to cover, been a while, this time as part of a project teaching portable shell programming to some wonderful, burgeoning programmers.

I've hit a question regarding, the securelevel startup window:

The system has to boot at securelevel -1 before it can raise. Does anyone know if that window has ever been exploited in the wild?
I'm trying to teach the gap between "must trust" and "trust nothing" and a real-world case would make it concrete.

Thanks in advance for any notes or urls!

Rocket-
.ike