Around 1400 passengers at Warsaw’s Chopin (Okecie) airport in Poland were grounded on Sunday after hackers allegedly attacked the computer system used to issue flight plans to the airplanes. The source of the attack isn’t yet known.

The alleged hack targeted LOT, the state-owned flag-carrying Polish airline. Reuters is reporting that the attack took place on Sunday afternoon, and was fixed about five hours later. 10 LOT flights were cancelled and about a dozen more were delayed, according to a LOT spokesman.

The spokesman didn’t provide any details of what had actually occurred, though he did give away this one tantalising morsel: “We’re using state-of-the-art computer systems, so this could potentially be a threat to others in the industry.” The spokesman said that flights that were already in the air were not affected by the hack and could land normally. Also, the hack didn’t affect the airport itself; it was just the LOT computers.