A couple of days ago, he forwarded a link to a paper that described how to hack wireless pacemakers. The paper, titled "Pacemakers and Implantable Cardiac Defibrillators: Software Radio Attacks and Zero-Power Defenses,"
describes how researchers at the University of Washington and the University of Massachusetts, Amherst first reverse engineered the protocols used to communicate with the pacemakers. They describe in detail how they used a software-defined radio to figure out the protocols.
Once they figured out how to communicate with the pacemakers, they devised a series of attacks and successfully pulled off a few of them. For example, they were able to disable a pacemakers "therapies," or actions the pacemaker is programmed to take in response to cardiac events. This attack basically disabled the pacemaker.
The paper concludes by suggesting several different ways to improve pacemaker security. If you currently have a pacemaker that is programmed with a wireless interface, you may want to take a look at this paper. Even if you don't, it's an interesting read.