Russian airline Aeroflot AFLT.MMcancelled dozens more flights on Tuesday but said it had now stabilised its schedule after a major cyberattack a day earlier.

Two pro-Ukraine hacking groups claimed on Monday to have carried out a year-long operation to penetrate Aeroflot’s network. They said they had crippled 7,000 servers, extracted data on passengers and employees and gained control over the personal computers of staff, including senior managers.

The Interfax news agency said Aeroflot had cancelled 59 round-trip flights from Moscow on Monday out of a planned 260. It said that a further 22 flights out of Moscow and 31 into the capital were cancelled on Tuesday.

Aeroflot’s online timetable showed that all but one of the 22 cancelled flights out of Moscow on Tuesday had been due to leave before 10 a.m. Moscow time (0700 GMT), but the schedule for the rest of the day appeared largely unaffected.

“As of today, 93% of flights from Moscow and back are planned to be operated according to the original schedule (216 return flights out of 233),” the company said.

“Until 10:00, the company carried out selective flight cancellations, after which Aeroflot’s own flight program stabilised.”

Apart from the many cancellations, Monday’s attack caused heavy delays to air travel across the world’s biggest country and drew anger from affected passengers.

Responsibility was claimed by the Belarusian Cyber Partisans, a long-established group that opposes President Alexander Lukashenko, and by a more shadowy and recent hacking outfit that calls itself Silent Crow.

Russian lawmakers said the cyberattack was a wake-up call and that investigators should focus not only on the perpetrators but on those who had allowed it to happen.