One of the four North Korean soldiers who defected to South Korea this year was found to have antibodies to anthrax, a bacteria that can be used as a biological weapon, according to South Korean television station Channel A Tuesday.

“Anthrax antibodies have been found in the North Korean soldier who defected this year,” said a South Korean intelligence official, who spoke to the station anonymously.

Having anthrax antibodies indicates that the soldier was either immunized against the bacteria or possibly exposed to it. The official did not indicate which of the four soldiers had the antibodies in his system.

Last week the Japanese newspaper Asahi reported that North Korea had started to test loading anthrax onto intercontinental ballistic missiles (ICBM). Through a series of tests this year, North Korea demonstrated the ability to theoretically strike anywhere in the U.S. with an ICBM. An ICBM shoots into space and its warhead is deployed before it comes crashing down through Earth’s atmosphere toward its target. The report said that North Korea was testing to ensure the anthrax weapon could survive the immense heat caused by the warheads re-entry.