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. 

According to the task force, the NIS was also involved in monitoring the activities of liberal politicians from the then-opposition parties, such as Seoul Mayor Park Won-soon and Sohn Hak-kyu, who headed the Democratic Party at the time.

The spy agency documented their surveillance information and reported it to the presidential office of the Lee administration, the task force added. Besides eavesdropping on the politicians, the report also included an analysis of how to use social networks for a political campaign.

“The report is designed to propose an election strategy for the ruling party’s candidates during general and presidential elections,” said the task force.

The political meddling scandal involving the NIS was revealed for the first time in December 2012 when the nation was gearing up for the presidential election. Former NIS chief Won was indicted in 2013 on charges of ordering an online smear campaign against opposition candidates, mainly then-presidential candidate Moon Jae-in, who is now president. 

Won was sentenced to three years in prison by the Seoul High Court in early 2015. But the Supreme Court returned his case to the lower court in July, saying the evidence that led to his conviction could not be seen as valid.

Prosecutors argued that Won was guilty based on emails retrieved from an NIS officer’s computer that contained hundreds of Twitter IDs and his instructions on online comments. But the top court overruled the claim, saying there was no evidence to substantiate the documents were written upon Won’s orders.