Calls are mounting for a prosecutorial probe into the nation’s spy agency, after it was revealed that it had operated a 3,500-member cyber team to manipulate public opinion during the Lee Myung-bak administration.

According to a special task force on the reform of the National Intelligence Service on Thursday, the NIS created as many as 30 units dedicated to posting online comments in favor of the then-conservative administration.

The units then hired more than 3,500 civilians to post such comments on portal sites, such as Naver and Daum, and social media, such as Twitter. The teams were created in May 2009 and continued their work until December 2012, when the candidate from Lee’s ruling camp, Park Geun-hye, won the presidential election, the task force said. 

The findings appear to confirm the allegation that the NIS abused its power to interfere with domestic politics and add weight to the suspicion that former President Lee and his presidential office greenlighted the illegal activities

Lee and his aides had yet to make any public comments as of Friday afternoon. The NIS chief at the time of the suspected activity, Won Sei-hoon, is currently on trial for meddling in the 2012 election. Prosecutors demanded a four-year jail term for him. The top court is to rule on Aug. 30.

“We believe (the revelation) is the tip of the iceberg, but still it is extremely shocking,” said Kim Hyun, spokesperson of the current ruling, liberal Democratic Party of Korea. “Those involved should come forward and tell the truth before it is too late.”

Dubbed “outer cyber teams,” the units consisted of civilians, such as retired military officers, office workers, housewives and self-employed entrepreneurs. They were paid up to 300 million won ($266,000) per month and worked under the NIS’ psychological operations department.