Italian Official: State of Alert in Europe

"Italy's European commissioner called the explosions in central London on Thursday a terrorist strike against Europe.

The Italian Foreign Ministry said at least two Italians were injured in the blasts, without giving details.

"What has happened is the tragic confirmation that terrorism strikes once more at the heart of Europe," said Franco Frattini, Europe's commissioner for justice and home affairs, in comments reported by Italian news agencies and confirmed by his office."
Yahoo

Dose anyone remember this:

"The North Atlantic Treaty Organisation (NATO), sometimes called North Atlantic Alliance, Atlantic Alliance or the Western Alliance,...

...The core provision of the treaty is Article V, which states:

The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all. Consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."
Wikipedia

And when exactly does it come into effect? What counts as an attack?