It has been reported by the Discovery News that an experiment showed that an implantable biomedical device could be hacked and had the settings changed. The device used in the experiment was a cardiac defibrillator, a device that sends small amounts of electricity to maintain a regular heartbeat. However, if the settings are changed, it may kill the patient.
The issue on security is being tackled by the developers, but they are assuring the public that it will be very difficult to hack an implantable biomedical device since the interface being used is not easily manufactured, so there is enough time to develop hack free devices.
(source)
