University of Minnesota researchers found flaw in AT&T and T-Mobile cell towers that reveals the location of phone users. The attack is most useful for determining whether a target is within a given geographic area as large as about 100 square kms or as small as one square kilometer. Attack can also be used to pinpoint a target’s location but only when the attacker already knows the city, or part of a city, the person is in. The messages contain I.D. codes.
Source: https://thehackernews.com/2012/02/how-hackers-can-track-your-mobile-phone.html