Aug. 5, 2013  -- The mysterious death of a San Francisco "ethical hacker," who was set to give a speech on infiltrating wireless implantable medical devices, has caused speculation that he was the victim of a targeted attack, and raised alarm about the safety of devices such as pacemakers.

Professional hacker Barnaby Jack, who famously demonstrated how to make ATMs spit out cash, was set to reveal the secrets of how implantable medical devices, specifically pacemakers, can be hacked, in a talk scheduled for last Thursday at the Black Hat security conference in Las Vegas.

"He was able to remotely exploit them, and this talk was really dedicated to how the manufacturers could improve the security of the device," IOactive CEO Jennifer Steffens said.

But his girlfriend found the 35-year-old dead in his San Francisco home July 25. The cause of death is still under investigation, according to the San Francisco coroner's office.

Police say they have ruled out foul play, but the cause of death might not be determined by the medical examiner for another month.

Jack dedicated his career to exposing the vulnerabilities hackers can exploit. The title of his scheduled talk at the Black Hat security conference was "Implantable Medical Devices: Hacking Humans," and he planned to discuss how these devices "operate and communicate, and the security shortcomings of the current protocols," according to the Black Hat website.

"He wanted to know, how could that stuff down there fail, and especially how it could fail if there were some not nice people out there trying to make it crash," security researcher Dan Kaminsky said.

Jack's research into the possibility of hacking medical devices is reminiscent of the plot twist in the end of the second season of the Emmy-award winning series "Homeland," in which the fictional vice president was killed when his pacemaker was hacked by terrorists.

That scene got people wondering whether it is possible to hack implantable medical devices. In an interview with Bloomberg News before his death, Jack said that the answer is yes.

"Once I took a look, I was actually shocked to see how many vulnerabilities existed," Jack said.

The FDA said in a statement that there is no cause for alarm for the nearly 3 million Americans who have pacemakers.

"[The FDA] is not aware of any patient injuries or deaths associated with these incidents, nor do we have any indication that any specific devices or systems in clinical use have been purposely targeted at this time," the regulatory agency said.

Meanwhile, questions -- and even conspiracy theories -- are swirling around the Web regarding Jacks' untimely death, with some even blaming the U.S. government.

"This is an industry where a lot of money and danger is at stake," ABC News consultant and former FBI Agent Brad Garrett said. "The work he was doing certainly put him at some risk," ABC News consultant and former FBI Agent Brad Garrett said.