Retirees from the National Intelligence Service(NIS) were found to have taken part in cyber activities to influence public opinion.
According to the spy agency's reform task force and prosecutors on Wednesday, there were as many as 150 people who engaged in psychological support activities for then NIS chief Won Sei-hoon as of 2012.
The number increased significantly from about 20 to 30 people in 2009.
They allegedly meddled in the presidential election by posting comments favoring then candidate Park Geun-hye.
An arrest warrant is being sought for the chief planning director of the NIS retiree association identified by his surname Roh.