An implantable medical device (IMD) includes communication circuitry that enables the IMD to communicate via a network such as the Internet. A security routine is executed on the IMD to determine whether the IMD is capable over communicating via the network. If so, the IMD requests an identifier of current firmware stored on a server that is connected to the communication network. The identifier of the current firmware is compared to an identifier of firmware that is installed on the IMD. If the installed firmware is the same as the current firmware on the server, a timer is reset, but if the installed firmware cannot be verified as matching the current firmware on the server (e.g., because the IMD is not capable of communicating via the network), the timer continues to run. When the timer expires, the IMD is prevented from communicating via the network until further action is taken.