Researchers from iSEC Partners recently demonstrated an attack on a Subaru Outback equipped with a vulnerable alarm system by using a computer to send alarm commands to unlock the doors and start the engine. This was possible because car alarms, GPS systems and other devices are increasingly connected to cellular telephone networks and can receive commands through text messaging. Devices that receive texts generally cannot refuse them and the commands encoded in them. Users can’t block texts; only operators of the phone networks can. If a secret phone number attached to a particular device is found, it can be thrown off by sending other commands through text messaging.