A senior Canadian analyst says the revelation that a navy officer based in Halifax sold secrets to the Russians is an indication of how weak military security is.

Canadians may never know the details of what went wrong at the navy intelligence center, HMCS Trinity, where Sub-Lt. Jeffrey Paul Delisle smuggled out information to the Russians on floppy disks and thumb drives.

The 41-year-old pleaded guilty in a Halifax court Wednesday to breach of trust and two counts of passing information to a foreign entity between July 2007 and Jan. 13, 2011, in Ottawa and Kingston, Ont., and Halifax and Bedford, N.S., where he lived.

'He clearly damaged Canadian national security, he may well have damaged the national security of some of our allies'—Wesley Wark

Delisle was posted to the security unit HMCS Trinity, an intelligence facility at the naval dockyard in Halifax. It tracks vessels entering and exiting Canadian waters via satellites, drones and underwater devices.

While there he worked on a system called the Stone Ghost linking the Five Eyes allies: the United States, Britain, Australia, New Zealand and Canada.

Wesley Wark, intelligence expert at the Munk Centre for International Studies, said he's not surprised the Russians were spying on Canada. What does surprise him is Delisle smuggled out secret information daily on an inexpensive thumb drive.

"Jeffrey Delisle was able to extract a lot of sensitive information from a site that was meant to be very highly secure," Wark said.

He said he's also surprised that Delisle's spying activities went undetected for at least four years.

Sub-Lt. Jeffrey Paul Delisle covers his face leaving a Halifax court Wednesday where he pleaded guilty to breach of trust and two counts of passing information. (Steven Puddicombe/CBC)

"Even if it had happened in the first place, it shouldn't have been allowed to persist," Wark said.

"He clearly damaged Canadian national security, he may well have damaged the national security of some of our allies… the real problem is the amateurishness of the security arrangements in places like Trinity and elsewhere that allowed him to walk away with so much material," said Wark.

He said this is an uncomfortable reminder of how vulnerable the national security system can be.