This post on F-secure raises the specter of German authorities tracking suspects through clandestine use of the SMS system. (The post references an article on Heise Online that translates to “Customs, Federal Police and Protection of the Constitution in 2010 sent more than 440,000 ‘silent SMS.'”
So what exactly does this mean?
Well, basically, various German law enforcement agencies have been “pinging” mobile phones. Such pings only reply whether or not the targeted resource is online or not, just like an IP network ping from a computer would.
But then after making their pings, the agencies have been requesting network logs from mobile network operators. The logs don’t reveal information from the mobile phones themselves, but they can be used to locate the cell towers through which the pings traveled. And thus, can be used to track the mobile targeted.