Some flights operated by Poland's national airline, LOT, were grounded on Sunday after hackers attacked its computer system.
The hacking attack targeted computers issuing flight plans at Warsaw's Okecie airport.
More than 1,400 passengers were affected, with 10 flights cancelled and another 12 delayed.
Services were getting back to normal on Sunday evening. The attack is now being investigated by airline authorities.
Flights to Dusseldorf, Hamburg and Copenhagen and Polish cities were affected, although LOT stressed that the glitch did not affect the airport or aeroplanes that were already in the air.
"We're using state-of-the-art computer systems, so this could potentially be a threat to others in the industry," said LOT spokesman Adrian Kubicki.
The source of the hack is not yet known.