Terrorists use online war games like "Call of Duty" to plot and discuss future attacks in private, an investigation by The Sun found.
Islamic extremists know cops monitor phone calls and emails, and turn to popular PlayStation and Xbox games to ensure their plans remain secret.
Online games allow players to log on in groups to play against each other and chat in private.
Once signed in to a "lobby" using a password, plotters then use Bluetooth headsets to speak securely to other users on the same site.
A source said, "It's a terrifying reality. These people waste no time finding a secure method of chatting. They are logging into group games over the Internet and discussing terror plots. Security people know about it."
Extremists choose realistic "first person" conflict games, including "Medal of Honor" and "Halo," because they can disguise their discussions as harmless web chat.
In the games, players work through a complex simulation of war scenarios, carrying out missions and battling enemy fighters.
News of the growing threat comes five years after the CIA first warned of the menace.
Different styles of play and missions -- from planting bombs to fighting one-on-one -- are available and players can even join "clans" -- groups which regularly play together.
There has also been evidence they are being used as training tools for insurgents.
Read more on this story at the Sun.