From ABC:

The latest design from al Qaeda's top bomb maker is a "belly bomb" developed to beat airport security in Europe and the Middle East where full body scanners are not widely used, according to U.S. officials.

A bulletin from the Department of Homeland Security warned, "DHS has identified a potential threat from terrorists who may surgically implant explosives or explosive components in humans to conduct terrorist attacks."

According to U.S. officials, the terrorist would detonate the bomb with a chemical-filled syringe.

"We do not think there would be enough to bring down a jetliner, but it is more likely the kind of bomb to be used in an assassination attempt," said one person briefed on the warnings.

U.S. officials told ABC News the "belly bomb" is the invention of Ibrahim Asiri, a young Saudi native who packed explosives into the rectal cavity of his 23-year old brother Abdullah for a suicide missions targeting the head of Saudi intelligence, Prince bin Nayef.

That bomb exploded prematurely, the officials said, and the only casualty was Asiri's brother. Asiri is also credited with two other failed plots involving the bomb hidden in the underwear of a passenger on a Detroit-bound flight, and the bombs hidden in printers being shipped from Yemen to Chicago.