You might say, "Of course, security has to be applied 24/7", but the obvious is not the standard. An example was given by Sebastian Klipper on his blog "Klipper on Security: Ps(i)2 - Sicherheit in Informationssystemen". Thanks for sharing the content of his post by CC license.
During the night, journalist Tommaso Cerno did a short trip to the airport of Rome and shared his experience on the web. The problem? There was no security at all. The screening lines and the security areas are freely accessible, doors secured by access codes or code cards are open, homeless people are taking a nap in the interior. Tommaso filmed the his tour through the airport and published it online:
http://espresso.repubblica.it/multimedia/home/22897704.
It would be an easy task to smuggle weapons or drugs into the airport during night. The only risk would be that one of the homeless people could find it before the next day and take it away, so Sebastian Klipper.
nice one :)