What was the bad, bad thing that Clear Channel did?

I have seen cited in several recent news articles from both the BBC and The Economist that Clear Channel was fined something to the order of $750,000 for some obsenity related offense on many of its stations.

Being involved somewhat as a DJ with a small radio station that may have occasionally slipped up in allowing an obscene word on the air, Clear Channel’s fine has piqued my curiosity. What exactly are they being fined for? Does anyone have any particular insight or commentary on the issue/fine?

Gracias

Apparently one of their DJs had a big potty mouth!