An administrator charged with responsibility for one or more administered wireless devices can use a wireless device to disable lost or stolen devices using an SMS lost-mode message. The data of the lost-mode message can be encrypted to prevent malicious attacks. The encrypted data may include a universal device identifier unique to the target device, the phone number of the administrator's device, and a time stamp memorializing command or message creation. Successful decryption authenticates the administrator. Before executing the lost-mode command, however, the target device reviews the unique identifier to verify the target and compares the phone number of the administrator's device with the number identified with the incoming SMS message to authenticate the relaying device. The target device can also consider an embedded time stamp to determine whether the lost-device command has been superseded.