NATO leaders agreed on Friday that a large-scale cyberattack on a member country could be considered an attack on the entire U.S.-led alliance, potentially triggering a military response.
The decision marks an expansion of the organization's remit, reflecting new threats that can disable critical infrastructure, financial systems and government without firing a shot.
"Today we declare that cyber defense is part of NATO's core task of collective defense," NATO Secretary General Anders Fogh Rasmussen told a news conference.
In 2007, a series of crippling cyberattacks paralyzed much of NATO member Estonia in an apparent response to a dispute over the movement of a Soviet-era war memorial. Most Western experts suspected the Kremlin was responsible but Russia denied it.
NATO backs plan to boost alliance's defenses
NATO leaders also approved a plan on Friday to boost the alliance's defenses in eastern Europe in response to Russia's intervention in Ukraine, Rasmussen said.
The plan, adopted at a summit in Wales, includes creating a "spearhead" rapid reaction force and pre-positioning supplies and equipment in eastern European countries so they can be rapidly reinforced in a crisis.
The initiative is intended to reassure former Soviet bloc states that have joined the U.S.-led the alliance, especially Poland and the Baltic states of Estonia, Latvia and Lithuania.
The allies agreed to hold the next NATO summit in Poland in 2016 in a symbolic gesture of support, Rasmussen said.
NATO says no third country can veto membership
NATO, responding to Russian warnings against Ukraine's bid to join the Western alliance, said on Friday that no third country could veto its enlargement policy and approved new steps to advance Georgia towards membership.