A major terrorist plot has been discovered in Britain to blow up aircraft in flight, so security lines are going to be very long. The targeted flights were believed to be heading to the United States. As a result of this, all US flights are on the highest possible security level.
All liquids and gels are temporarily banned from carry-on luggage.
This does bring up the obvious question, why isn't airport security always on the highest possible level? I know it's a pain in the ass, but it does beat being dead.