Police hired a cyber security firm as part of a year-long investigation into alleged Twitter trolling by PSNI staff.
Experts were used to help identify the individuals behind several accounts which also appeared to reveal information about ongoing police operations.
The PSNI confirmed on Monday that it was conducting a probe into online activity by people purporting to be police officers.
It has emerged that an internal review was launched a year ago, shortly after Chief Constable George Hamilton faced criticism for comments he made via social media to an officer.
Mr Hamilton apologised after he told an officer to stop "wallowing in self pity" and "dry your eyes" in a Twitter exchange last August.
The officer had raised concerns about growing pressures of the job.
A number of anonymous Twitter users, suspected of being police staff, subsequently criticised the PSNI chief and posted complaints about the job and the organisation's management.
A parody recruitment video was also produced and posted to YouTube by one of the individuals under investigation.
The video shows a number of PSNI officers dancing beside a police helicopter and at other sites across Northern Ireland.
A voiceover says, "Are you considering a career where every day you drive home you fear you will be shot? Do you want the rush of wondering if the IRA has planted a bomb under your car? Do you want to be told to dry your eyes when asking for mental health support?
"Then join the Police Service of Northern Ireland today. Recruitment is now open to a host of new officers to be belittled by senior management teams, spat on by the public, harassed by the police ombudsman and have their spirits crushed."
A security source told the Press Association that the account that began to cause the greatest concern to management was being run under the Twitter handle @DonYeeoo because of alleged racist and sectarian comments, trolling of other social media users and sharing of classified police information.
A number of the anonymous accounts which formed part of the internal probe were suspended last week.
It is understood investigations are still ongoing.
PSNI assistant chief constable Mark Hamilton recently said police are "examining material posted on personal social media accounts by a number of individuals and are undertaking investigations to establish if the individuals are all serving officers."
On Monday, the PSNI said the organisation "will not accept any racist, sectarian, sexist or homophobic behaviour from any of our staff."