Japan Airlines said it was hit by a cyberattack on Boxing Day, causing flight delays and disruption—here’s what we know so far.

Japan Airlines (JAL) (9201.T), opens new tab said on Thursday its systems returned to normal, with same-day ticket sales resuming, after a cyberattack delayed some domestic and international flights.

Japan Airlines said it was hit by a cyberattack Thursday, causing delays to more than 20 domestic flights but the carrier said there was no impact on flight safety. JAL said the problem started Thursday morning when the company's network connecting internal and external systems began malfunctioning.