Japan Airlines (JAL) said on Thursday that its systems were back to normal after an alleged cyberattack crippled its servers and halted ticket sales. This comes only days after American Airlines, one of JAL's partners, experienced a crippling Christmas Eve ground stop.

The attack began at 7:24 a.m., when the company's software connecting internal and external services became overwhelmed. Such an attack is known as a Distributed Denial of Service (DDoS) and occurs when a system is overwhelmed with large amounts of data to the point where it becomes inoperable.

As a result, same-day ticket sales were halted and luggage handling operations were interrupted.

No customer data was leaked, according to the airline, and the system is believed to be unaffected by any malware. Same-day ticket sales have also returned to normal, but the standby and upgrade systems have been suspended, per a post on the airline's X page.

The standby system coordinates the listing of passengers without a seat assignment, whether it be unconfirmed passengers looking to change their ticket, or airline employees flying on a discounted ticket. The upgrade system allows gate agents to reassign seats to certain passengers in more premium cabins.

According to the Associated Press, experts have repeatedly raised concerns about the integrity of Japan's cybersecurity systems, especially as the country begins working more closely with foreign governments. Although Japan has made efforts to improve its security, experts say more work is needed.

Holiday Travel Disruptions: a Busy Period for JAL

This comes at a busy time for airlines, as hundreds of millions of holiday travelers look to catch flights home. Flight delays and cancellations during a peak travel period could cause a snowball effect, leading to further disruptions for travelers on later flights. Flight tracking service FlightRadar24 shows that operations have mostly returned to normal, with an average delay time at Tokyo's Haneda and Narita airports of 20 minutes and 16 minutes, respectively.