DEARBORN, Mich. (AP) — Students in a suburban Detroit seventh-grade history class were expecting a video on explorers Lewis and Clark, but instead viewed at least 30 seconds of pornography.

WJBK-TV reports that a substitute teacher at O.L. Smith Middle School in Dearborn eventually was able to turn the computer off.

Dearborn Public Schools says the March 13 incident was caused by a technology glitch. District spokesman David Mustonen says officials are looking into the incident to make sure it doesn’t happen again.