March 23, 2012: The U.S. Army is warning its troops to be careful what they post to on social networking sites (like Facebook). When they post photos of themselves they often reveal militarily useful information. This was discovered in Iraq, where a lot of tech savvy people working with terrorists were able to compile information from what troops posted. This sometimes led to attacks, and this was discovered from interrogating captured terrorists and captured documents and computer data. The background of pictures often indicated targets for the terrorists, or details of base defenses and American tactics. Islamic terrorists have been quick to use the Internet and other modern technology to plan and carry out their attacks.
Some of this technology can be very dangerous, like the geo-locating capability of many smart phones (which include GPS receivers and location data that hackers can obtain). Troops in combat zones are ordered to turn geo-locating off while in areas where the enemy could use it. Even without geo-locating turned on, cell phone use can provide militarily useful information. This goes back to a century old practice called traffic analysis. This has been used with great success against terrorists in Iraq, Afghanistan, and elsewhere but it can be used against the troops.
Traffic analysis use against terrorists was not revealed for as long as possible. But it eventually came to light when people wondered how the U.S. government could issue so many warnings of possible terrorist attacks. The government rarely revealed where the information came from. This was standard practice, as any sources inside or close to al Qaeda would not last long if it were revealed they were passing on information. But most of the information obtained did not come from sources in al Qaeda but from traffic analysis.
When all you can do is detect enemy messages, without being able to read them (because it is coded or not a strong enough signal to read), you can learn a lot from how many messages there are and where they are coming from. This is a technique that first became widely used during World War I (1914-1918).
U.S. intelligence agencies have compiled a lot of data on how al Qaeda communicates via phone, the Internet, couriers, and mail. A decade ago deals were being made with foreign governments to try and detect, and then collect, messages from possible al Qaeda sources. Since then a general increase in al Qaeda messages ("chatter") and bits of data that has been read from some of those messages, was the basis for many terror alerts. This was classic traffic analysis. It wasn't perfect, but in past wars it provided valuable and lifesaving information. But because it's imperfect information you can expect a lot of false alarms.
Al Qaeda was long suspected of knowing how to manipulate message traffic in order to deceive our traffic analysis methods. This was rarely the case, but this form of deception has been used in the past with success. For example, when the June 6, 1944 D-Day invasion of France was being planned a fake army group headquarters was set up in England. Actually, this "army group" consisted largely of a lot of radio and telegraph operators sending a large number of messages that would be normal if the "army group" were preparing for an invasion of France, in an area other than where the actual invasion was going to take place. The deception worked. German traffic analysis experts were fooled and the Germans believed the actual invasion at Normandy was just a feint, a move to get the Germans to send their reinforcements to Normandy rather than where the fake "army group" was going to invade.
Intelligence agencies have to be constantly on guard for al Qaeda, or any other terrorist group, using this kind of deception. It has happened in a few instances, so a larger-scale attempt is not out of the question.