Victoria Police is investigating one of the biggest information leaks in the force's history after documents containing sensitive details of individuals were found at three Melbourne properties.
A junior police officer from the northern metro region has been suspended without pay.
Police said one of the properties containing the police documents was linked to bikie gangs.
Chief Commissioner Ken Lay told reporters the leak was "one of the gravest breaches of police security".
"Certainly in my time in Victoria Police I have never seen anything quite like this," Lay said.
Police said the files were between two months to three years old.
Victoria Police told SC it could not reveal how the documents were leaked nor whether they were found in hard copy or stored on electronic media.
However the breach follows a series of scathing reports by the Commissioner for Law Enforcement Data Security, David Watts, into Victoria Police's data security.
The most recent report for 2011-2012 found Victoria Police "struggles to fulfill" appropriate and consistent data classification and that all reviewed systems "raised serious concerns regarding the assessment of the sensitivity of the information held in each system and the adequacy of the security controls employed to protect that data in accordance with its sensitivity".
Concerns were also raised for Victoria Police's intelligence and case management system, Interpose, which contained information relating to ongoing investigations along with intelligence reports and sensitive data about individuals.
Commissioner Watts told SC he would wait for the completion of the Victoria Police TaskForce Eel, formed to investigate the breach, to determine if his recommendations to improve security in the force had been applied.
"We will wait to see for the Taskforce to complete its investigations [before] we will consider taking action," Watts said.
"We have looked into security of LEAP (Law Enforcement Assistance Program) and Interpose in the past and would be interested to see how they relate to the recommendations."
Watts will meet with commissioner Lay for updates on the incident.
Security improvements were made over the last 12 months to Interpose and across Victoria Police following more scathing previous reviews by the Commissioner which detailed "problems that have plagued [police] information management, security and ICT systems for more than a decade".
The Commissioner also found that security improvements could be made on new systems, but were not done on older systems.