From a story on how airlines are now profiling passengers:

Airline-security personnel say the evolving profiling system is likely to take into account such factors as how an individual’s ticket was purchased, the clothes the passenger is wearing, the person’s nationality, travel history, and even the book that he or she may have just purchased at an airport shop. In addition, travelers are likely to be subject to closer surveillance at airport terminals and searched more routinely.

http://www.msnbc.com/news/646421.asp