TALLINN, Estonia — In the six months since part of Ukraine’s power grid came crashing down, turned off by highly sophisticated hackers, cyberspace allies of President Vladimir V. Putin of Russia have been leaving their mark here in the Baltics and across the sea in Finland and Sweden.

Perhaps to discourage the traditionally neutral Finns and Swedes from growing closer to NATO — this past week NATO conducted a naval exercisefrom Finnish territory for the first time — hackers disabled the Finnish Ministry of Defense’s website. That was preceded by electronic espionage against a Dutch commission that had concluded that a Russian-made Buk missile brought down a Malaysian airliner two years ago, killing 298 people. And Germany’s intelligence agency, the BND, recently told American officials that it believed Russian hackers had been behind a cyberattack that destroyed a German steel mill.

Source: As Russian Hackers Probe, NATO Has No Clear Cyberwar Strategy