The military and the National Intelligence Service are investigating massive leaks of secret weapons technology over past years from the Agency for Defense Development.

Researchers are suspected of habitually stealing hundreds of thousands of such secrets when they resigned or retired from Korea's leading agency for defense technology development.

The ADD has spearheaded the country's weapons development from missiles to aircraft and tanks since its establishment in 1970.

"The Defense Security Support Command has been conducting an investigation of some 60 former senior ADD researchers in cooperation with the National Intelligence Service and police over the theft of secrets when they resigned or retired from the ADD," a military spokesman said on Sunday.

"The investigation specifically focuses on about 20 former ADD researchers who left the agency in the last two or three years."

One researcher who left the ADD last September then landed a job as a senior fellow at a private university in Seoul and is suspected of stealing a whopping 680,000 pieces of secret information, from drone and other weapons systems to artificial intelligence technologies.

Most of the 20 landed jobs at domestic defense firms. Some have confessed that ADD staff habitually stole tech secrets to help them land another job when they left.

"We're trying to find out what and how many technologies were leaked to where," a military spokesman said.

An ADD official said, "We are taking this case very seriously and need to find out if technologies can be better protected."