Authorities were saying that the explosive device failed. Gratefully no one was seriously hurt and the plan, if there was one I assume, didn't go off as it was supposed to.
http://www.usatoday.com/travel/flights/2009-12-25-airliner-disturbance-detroit_N.htm
http://www.usatoday.com/travel/flights/2009-12-25-airliner-disturbance-detroit_N.htm