In 1971 Britain expelled 105 Soviet diplomats, which though a greater number still was a unilateral move, Juurvee pointed out. "That so many states do it at once hasn't happened before, and will certainly be a lesson and have practical importance at least up to a degree," he added.

Experiences of the Cold War showed that if only a single country expelled diplomats working for Russian security services, the officers posted to neighboring countries could take on their tasks without much difficulty.

But if this is done across several countries at once, the move is more likely to cause problems for Russia, Juurvee said.

While in earlier cases diplomats were usually expelled after certain names were brought up by a local security authority, in this case it was a political decision followed by a gathering of information who exactly should be expelled.

"That Russia presents a danger in terms of intelligence isn't new, this phenomenon is soon 100 years old, and naturally it's the task of counterintelligence to keep an eye on what the embassies of other countries are doing," Juurvee said.

Despite the chance of success of the current coordinated move of Western countries, in the realm of intelligence there is no final victory or defeat, Juurvee cautioned. "Every setback or victory is temporary," he added.

As far as Russia's reaction to yesterday's announcements is concerned, Juurvee expects Russia to respond in kind and expel a similar number of diplomats in turn.