The story of Jeffrey Delisle's treachery has made few headlines outside of his native Canada - yet the actions of the Naval intelligence officer may have potentially serious security implications for the UK.
Jeffrey Delisle walked into the Russian Embassy in Ottawa the day he found out his wife was cheating on him.
It took five years for his betrayal to be discovered.
But now that it has been, it has rattled the wider intelligence community of English-speaking allies.
Officials in London are tight-lipped about the precise secrets that Delisle may have spilled that affect British national security.
On the record one official would only say the government was "aware" of the case.
But off the record it is clear that British officials in government and the intelligence agencies have taken an interest in the case at the highest level.
The reason is that even though Delisle was a Canadian spy he also admits he was passing British secrets and in the process may have done real damage to trust among allies.
Codename 'Stone Ghost'
Delisle pleaded guilty in October to passing sensitive information to the Russian military intelligence service.
"It was never really Canadian stuff," he told police after his arrest in January, according to a report in Canada's Globe and Mail newspaper.
"There was American stuff, there was some British stuff, Australian stuff - it was everybody's stuff."
When Delisle discovered his wife was cheating on him, he walked into the Russian Embassy.
"I said: 'Here I am.' It wasn't for money. It was never for money," he later claimed, although he was paid around CDN$3,000 ($3,000; £1,900) per month.
He would download secrets from his office computers onto a floppy disk, then transfer them to a memory stick before taking this home and loading the data up into a private email account, saving it as a draft.
A Russian handler then logged in to the email account to retrieve the information.
Delisle had access to a system codenamed Stone Ghost.
This is a computer network that shares information between the English-speaking intelligence allies - the US, UK, Canada, Australia and New Zealand.
Much of it is thought to be technical and signals intelligence of the type collected in Britain by GCHQ and used by the military.
No-one seems sure exactly how much Delisle purloined from the database.
But given he was spying for years the damage is potentially massive.
His role at the Trinity base in Nova Scotia may be particularly significant, according to one UK based official.
Trinity brings together intelligence from a number of sources on maritime surveillance - watching the Atlantic for suspicious activity, including submarines.
During the Cold War, allies invested enormously in building up a network of undersea acoustic arrays and satellite capabilities to detect Soviet subs.
That capability atrophied at the end of the Cold War, but recent years have seen governments discussing the need to renovate the system to spot submarines in the Atlantic and also the Arctic.
According to one report in 2011, the Canadian Navy was already in discussion with the US Navy and Royal Navy about co-operation.
If details of these capabilities were passed on by Delisle they would be highly valuable to the Russians, allowing them to take counter-measures to avoid being spotted, potentially wasting a huge amount of effort.
The Russians seems to have especially wanted details of human agents but Delisle may not have had much access to this.
But it is in the impact on trust among allies where the greatest damage may be, according to a British source.
A Canadian official conceded to the BBC that the case was very significant but was at pains to emphasise that Delisle had been dealt with.
British intelligence officials say that one of their worst nightmares is a mole like Delisle who spills classified secrets of allies - particularly those of the United States.
Given the much greater size of its intelligence agencies, allies know they need the US more than the US needs them.
The US may have the odd mole itself but no-one would dare suggest cutting the Americans out of the relationship, yet if the Americans fear too many leaks from allies then they might restrict what they share with serious consequences.
"If we lose information from our allies we might not get that indication of an impending terrorist attack… I think this is going to push us back to the Stone Age." Canadian officials feared, according to the Globe and Mail newspaper.
The Delisle case also underscores the worry some intelligence officials have about the security of computer networks - especially among allies.
The Wikileaks case - in which one soldier allegedly downloaded vast amounts of diplomatic traffic stored on a single database - highlighted the dangers when information is collected into one place where relatively low-level staff have access.
Most intelligence agencies (including the UK's) place restrictions on the use of memory sticks on classified computers and also carry out traffic analysis to look for the suspicious downloading of data or unusual searches.
But when intelligence is shared among allies, all that matters is a breach at the weakest link in the chain for other people's secrets to escape.
Canada will be facing tough questions from allies about what went wrong.
So how much damage has the case done? No-one is saying partly because they may not know since Delisle was only discovered years into betrayal.
And his guilty plea means there will be no trial in which what is known comes out.