Details are sketchy at the moment, but he was doing something suspicious in the bathroom on the plane.
The report says it may be he did nothing worse than smoking on the flight. However the same report suggests when questioned, he said he was trying to blow the plane up with a shoe bomb. If he was being cute, then I bet he regrets saying that now.
The terrorists, that is.
So here's what we've come to? We've been taken hostage already.