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.

Flight plan computers do exactly what they say on the tin: they produce the exact route that the airplane will take to its destination. An optimised flight plan factors in hundreds of variables, from weather conditions, to the expected take-off weight of the plane, to various air traffic control requirements, with the ultimate goal of reducing fuel consumption and minimising the risk of mid-air collisions.

In theory, it is possible to draw up flight plans manually, but a large airline like LOT probably mandates that the computers are used for safety reasons—and so when it was compromised by hackers, some kind of lockdown protocol triggered. It's worth pointing out that, at this time, there's no confirmation that this was actually a case of hacking: LOT's system might have just encountered some kind of catastrophic software bug, with the engineers wrongly attributing it to hackers.

The LOT spokesman said the attack is being investigated by authorities. If other airlines do indeed use the same flight planning system as LOT, we could be in for a bumpy ride. Earlier in June, United flights in the US were grounded due to a possible hack of its flight planning system.