Act of War: Hackers attack Polish airlines

Today, around 4p.m. (local time) the hackers attacked (ground) IT systems of Polish Airlines, LOT. They attacked a planning system without affecting the planes' systems.

If the attack was sponsored by Russia, would that be an act of war?

The Guardian: Hackers ground 1,400 passengers at Warsaw in attack on airline's computers

ABC Online: Hackers ground 1400 LOT passengers at Warsaw airport

Business Standard: Polish airline cancels flights after hacker attack