With the right kit and a little know-how, it is possible to hack into a pacemaker and take control. According to US researchers from the Medical Device Security Center, this is feasible because many pacemakers contain a radio designed to allow reprogramming of the heart-control devices.

The radio's signal is unencrypted, allowing a malicious attacker to turn off the pacemaker completely or deliver a shock to the heart which would cause ventricular fibrillation and thereby a cardiac arrest. The kit required is specialist and expensive, and an attacker would need to be in close physical proximity to the victim, but the possibility is very real.

The researchers didn't test on a live pacemaker wearer. Instead they put the target device into a bag of meat, which is much the same thing. The link below will take you to a PDF of the research paper.

Research Paper [Secure Medicine via the Register]