In a Sunday report in The Guardian newspaper, government officials are said to have flown to Belfast, after the USB stick was found in a local car park and offered to a newspaper.
When the USB stick - which appears to have contained 37 pages of data on Royal Staff, including their names, ages and ranks - was rejected by the paper, it was handed in at a local police station.
Staff from Portsmouth naval headquarters are said to have flown to Belfast to investigate the incident and establish the last known user of the USB memory stick.
According to the newspaper report on the incident, investigators are looking at the electronic footprint of the USB stick, as well exploring the "possibility that personnel from the Hunt class mine counter-measure ship accidentally dropped the memory stick while away from the vessel".
Commenting on the story, Jason Holloway, SanDisk Enterprise head of sales for Europe said that, although the USB memory stick was found and handed in, it's unknown if the restricted data on the device was copied.
"It's likely that the data was accessible, as it was offered for sale to a newspaper before the stick was returned", he said.
"This shows why it's essential to hardware-encrypt data copied onto USB flash drives, and to make that encryption automatic and transparent to users, so they can't short cut the protection", he added.
"Many organisations are banning the use of personal, unauthorised USB devices and issuing key staff with managed, secure drives that can be audited - and terminated - if lost. This gives the benefits of using flash drives without the security risk."