But Canadian Security Intelligence Service director Dick Fadden says he can't guarantee that Sub-Lt. Jeffrey Delisle will be the last insider to betray sensitive secrets.
"This is one case that we caught. I suspect there will be others over time, both here and within our allies," Fadden told a Senate committee Monday.
Delisle, 41, was sentenced last week to 20 years in prison after pleading guilty to handing classified material to Russia in exchange for cash for more than four years.
"Do I think that this is catastrophic? No, it's not," Fadden said. "Is it something to sort of say, 'Oh, it happened, it'll go away?'
"Neither — it's somewhere in the middle."
Based most recently at an intelligence centre in Halifax, Delisle had access to information shared by the so-called Five Eyes allies — Canada, Britain, the United States, Australia and New Zealand. Delisle used floppy discs and USB drives to smuggle the closely held data out of the facility.
"I think what saves us — if that's the right word — in these instances with our allies is that every single one of them has been in the same situation before," Fadden said Monday. "Having said this, I think there's a consensus amongst ourselves and our close allies that this has been to some degree the straw that broke the camel's back.
"And it's caused ourselves and a number of our close allies to review the security arrangements that have been in place within our countries and between our countries."
Delisle's top secret-level security clearance was up for renewal months before he transferred to Halifax in 2011, prompting questions about whether such a check would have uncovered the fact he had serious personal difficulties.
Fadden said that if a person's security clearance expires, they are allowed to continue working with sensitive data "unless there's a reason why we think they should be removed while we continue the security clearance."
The CSIS director insists there was no red flag with Delisle in any event.
"He was divorced, he was having financial problems, and his family was breaking up. That probably defines a large part of the Canadian population, unfortunately," Fadden told the senators.
"So they alone, I don't think, would have been enough for a red flag to have flashed. I think in retrospect an orange flag would have been worthwhile. But he didn't do anything obvious that would lead either ourselves or the Defence Department to believe he was a traitor. He sort of chugged along, he was a relatively quiet guy, didn't make a big fuss."
Fadden said he wishes he could assure Canadians a case like Delisle's won't happen again. "But I can't."
He acknowledged that Canadian security officials don't know the full extent of what Delisle gave to the Russians through an Internet account. "The technique that Delisle used allowed him to effectively eliminate the material transferred after it had been received."
The spy chief said he has been working with deputy ministers who have national security responsibilities to tighten procedures in the electronic and physical realms, as well as in the area of security clearances.
"We've looked in some detail at what happened in the Delisle case," he said.
"In virtually every instance, there has been — or there is in the process of being — some tightening up."
The Defence Department said last Friday following Delisle's sentencing that security is being improved, but provided no specifics.