Missing sections of a PSNI notebook which fell from a moving car contained details of 42 officers and staff, police have confirmed.
Assistant Chief Constable Chris Todd said those affected had been made aware.
The incident occurred on a stretch of the M2 motorway in north Belfast on Thursday when a laptop and a notebook fell from a police car.
It came just a week after the PSNI confirmed a major data breach after the personal details of more than 10,000 officers and staff were mistakenly published online.
Mr Todd said: “Police are continuing to investigate the loss of an officer’s laptop and notebook.
“It is believed the material fell from a moving vehicle on the foreshore stretch of the M2 motorway, on Thursday August 17 around 4.15pm.
“The laptop was immediately deactivated and has since been recovered.
“No personnel files were involved.
“A significant amount of the notebook has since been recovered.
“Some sections remain outstanding and our inquiries are continuing to establish the contents.”
He added: “This afternoon, it was confirmed that some of the outstanding pages, which contained details of some officers and staff, have not yet been recovered.
“We have contacted those involved to make them aware.
“Forty-two officers and staff have been specifically identified as being affected and directly contacted last night by line managers and senior management.
“In addition, the entire branch affected has been informed about the circumstances of the incident.
“We are liaising with the Office of the Information Commissioner and have advised the Northern Ireland Policing Board and the Department of Justice.
“Anyone with information or who recovers any material is asked to contact police on 101.”
Last week, the force was rocked by a massive data leak after it revealed the document had mistakenly been shared online in response to a freedom of information request.
Details released included the surname and first initial of every employee, their rank or grade, where they are based and the unit they work in.
On Monday, PSNI Chief Constable Simon Byrne said he believed the information was in the hands of dissident republicans.
It followed the posting of documents from the leak on a wall near a Sinn Féin office in Belfast.
Many officers have expressed concern for their safety in Northern Ireland, where police are under threat from terrorists – with the current level of threat assessed as severe, meaning an attack is highly likely.
Earlier this year, dissident republicans were blamed for the attempted murder of Detective Chief Inspector John Caldwell.
The Policing Board, which has oversight of the PSNI, is to hold a follow-up meeting on Tuesday to receive an update on the data leak and to consider further actions necessary.
Last week, the PSNI also revealed that in a separate incident, a document containing the names of officers and staff was stolen along with a police-issue laptop from an officer’s car on July 6th.
