A more subtle way to communicate with the mother ship would be to ship an update that makes the CPU leak some desired information. For example change how some s

A more subtle way to communicate with the mother ship would be to ship an update that makes the CPU leak some desired information. For example change how some specific cryptographic operation works under certain conditions to make it possible for eavesdropper to break the encryption. Or just make some funny things with memory and make certain information available to be retrieved via web browser when user visits malicious page.