The investigation into the lost notebook is not the first such inquiry the PSNI has had to launch.
In July, police had to inform people and business owners that their private data may be in the hands of suspected loyalist paramilitaries.
The information was thought to have been unintentionally given to loyalists subject to investigation.
A number of computer devices were removed during an investigation for forensic examination as part of a police inquiry before being returned to the owners.
However, a pen drive containing what is thought to be a `configuration file', containing personal details of private citizens from a number of internet service providers, was left in one of the devices.
In February 2012, there were calls for PSNI officers to be banned from carrying personal phones while on duty following a major security breach, which was revealed by The Irish News.
An investigation was launched by police after the newspaper revealed that Oglaigh na hEireann, which has targeted police officers, had the personal phone of an officer based at Grosvenor Road station in west Belfast.
The group, which used a recognised codeword, claimed to have had the phone for more than a year and to have "gleaned whatever information needed" from it.
The investigation involved senior officers from the Serious Crime Squad based in North Queen Street in Belfast.
All colleagues of the female officer whose pictures were on the phone were warned about the potential threat to their personal security.
Two months later, the PSNI launched an internal investigation after an officer left a gun behind on a child's bed during the search of a family's home in north Belfast.
The handgun and holster lay in the child's bedroom for almost 30 minutes before red-faced officers returned to the house to retrieve the weapon.
The blunder happened when police arrested an election agent for the Irish Republican Socialist Party and then searched his home in Ardoyne.
Thirty minutes after police had finished the search and left, two officers returned to the address revealing they had "forgotten something" and went upstairs to retrieve the gun.
