An unknown group of hackers infiltrated an airline's flight plans and temporarily grounded an estimated 1,400 passengers at Warsaw’s Frederic Chopin airport on Sunday.

The Polish airline, LOT, fell prey to what was most likely a distributed denial of service (DDoS) attack -- when a system is so bombarded with communication requests that it overloads the server and it can no longer function normally.

"As a result [of the attack] we’re not able to create flight plans and outbound flights from Warsaw are not able to depart," LOT said in a statement on Sunday. "We’d like to underline, that it has no influence on plane systems. Aircrafts, that are already airborne will continue their flights. Planes with flight plans already filed will return to Warsaw normally."

Some of the passengers were able to board their flights later in the day and as of Monday morning, the airline was back to regular service.

As planes become more and more connected to the Internet, concerns arise about the possibility of hacking threats. LOT chief executive Sebastian Mikosz warned that an attack like this could happen to other airlines.

So far there isn't enough detailed information on the attack available to fully understand how it ocurred or for the culprits to be known. Most often denial of service attacks are carried out on a public website, but the LOT system doesn't have one.

Andrey Nikishin, Director of Future Technology Projects at Kaspersky Lab, told ThreatPost that until we know for sure, this attack has many possible explanations. Human error, a technological malfunction, or the beginning of a larger attack are all options.

Earlier this year a researcher tweeted that he was able to hack into the communication system of his United Airlines flight. Since then the FBI has started an investigation into his claim.

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