Some of Europe’s biggest airports, including the region’s busiest Heathrow, raced on Sunday to restore normal operations to automatic check-in systems after disruption caused by hackers a day earlier.

The hacking incident hit check-in and boarding systems provider Collins Aerospace, owned by RTX, disrupting operations on Saturday at London’s Heathrow, Berlin Airport and in Brussels, where passengers faced long queues, dozens of cancellations and delays.

Disruption had eased significantly by early Sunday despite some continuing delays, airport officials and data showed, while regional regulators said they were investigating the origin of the hacking incident.

The disruption is the latest in a string of hacks to hit sectors from healthcare to autos. A breach at carmaker Jaguar Land Rover halted production, while another caused Marks & Spencer losses in the hundreds of millions of pounds.

RTX called the incident a “cyber-related disruption” and said it had impacted its MUSE software, which is used by several airlines. RTX was not immediately available for comment on Sunday.

Berlin Brandenburg Airport said on Sunday that problems persisted, but that it was working with the company to resolve the issue. A manual workaround is in place, and there are currently no major delays or cancellations, it added.

Brussels Airport said in an update to passengers on Sunday that the cyberattack was having a “large impact on the flight schedule”, causing delays and cancellations of flights.

Heathrow said early on Sunday work was continuing to recover from the check-in system outage. It added that “the vast majority of flights have continued to operate”.

An analysis by aviation data provider Cirium said delays at Heathrow were “low”, Berlin had “moderate” delays, while Brussels had “significant” delays, but that they were decreasing.