This is a well known technique. Law enforcement and mobile operators routinely use silent SMS to triangulate phone location. Smartphones now make it easier to c

This is a well known technique. Law enforcement and mobile operators routinely use silent SMS to triangulate phone location. Smartphones now make it easier to capture a lot more than just location. We know of several groups that sell turnkey exploits/malware (to governments as well as other parties). There is unfortunately no way to block silent SMSes without disabling the entire messaging service (this is by design).