OPSEC
All terrorists practice a high level of OPSEC since their need to be secret is how they can be successful. Whether it is the al-Qaeda training manual, online magazines targeted for the world, or the training of youth in Jihad camps, OPSEC is one of the first priorities for terrorists.
Secure communications are big as well. The September 11 hijackers, for example, accessed anonymous Hotmail and Yahoo! accounts from computers at Kinko's and at a public library. Messages are also coded. Three weeks before the attacks, Mohammad Atta reportedly received a coded email message that read: "The semester begins in three more weeks. We've obtained 19 confirmations for studies in the faculty of law, the faculty of urban planning, the faculty of fine arts, and the faculty of engineering." The faculties referred to the four targets (twin towers, Pentagon, and Capitol)
The list of methods goes on and on and is very similar to the methods used in organized crime around the world.
Read more about this topic: Information Operations