The 28-year-old official from the National Intelligence Service (NIS), identified only by her surname Kim, is suspected of trying to manipulate public opinion ahead of the Dec. 19 election by posting negative comments about Moon on the Internet using multiple user IDs.
Kim, who has denied the allegations, entered the Suseo Police Station in southern Seoul without answering any questions from reporters.
The scandal broke just days before the vote, emerging as a major campaign issue for both Moon and his then-rival, Park Geun-hye of the ruling Saenuri Party, who went on to win the race. The main opposition Democratic United Party (DUP) blamed the government and the ruling party for what they said was a manipulation of public opinion, while Park flatly rejected the allegations and accused the opposition of violating the agent's basic human rights.
Three days before the election, police announced they were unable to find evidence backing the allegations.
Police, however, said Wednesday that they found evidence the NIS agent had "recommended" or "disapproved of" certain online posts related to the presidential race.
Kim allegedly used 16 different user IDs to click on corresponding buttons about 200 times between August and December, according to the police. The posts she clicked on were mostly politically published on progressive Web sites.