(WXIA) - The Food and Drug Administration said some pacemakers have been hacked.

There are half-a-million people out there with pacemakers vulnerable to hackers who might be able to switch off the devices.

The threat is so serious, the FDA is recalling those implantable pacemakers.

"These devices are implanted under the skin in the upper chest area and have connecting insulated wires called "leads" that go into the heart. A patient may need an implantable cardiac pacemaker if their heartbeat is too slow (bradycardia) or needs resynchronization to treat heart failure," according to the U.S. Food and Health Administration.

The pacemakers in question are Abbott, formerly St. Jude Medical's (RF)-enabled St. Jude Medical implantable pacemaker.

The Firmware which is software embedded in the device can be updated. Patients are encouraged to contact their doctors.

For more information, there's a toll-free number you can call for details: 1-800-722-3774 or visit www.sjm.com/cyberupdate.