Flights and airport operations were not affected in attacks that impacted several other airports including New York, Atlanta, and Los Angeles.

On Monday, October 10, the websites at O’Hare and Midway International Airports were knocked offline by hackers tied to pro-Russian cyberattack groups. Airport websites of several other cities were also shut down.

Flychicago.com and other websites connected to O’Hare and Midway international airports were offline until about noon, according to a statement from the Chicago Department of Aviation.

No flights were affected. Nor were other airport operations. Website access has since been restored.

The attack hit the sites of several other U.S. airports, including LaGuardia Airport in New York, Hartsfield-Jackson International Airport in Atlanta, and Los Angeles International Airport.

The attack was coordinated by a pro-Russia hacker group known as Killnet.

The group posted a list of airports on Telegram, urging hackers to participate in what’s known as a DDoS attack — a distributed denial-of-service caused when a computer network is flooded by simultaneous data transmissions.

The group’s call to action included airports in Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, and Missouri.

It was not immediately clear how many of these airports were actually hit or whether all the sites suffered any disruptions.

The attacks come on the heels of another wave of cyberattacks allegedly launched by the same group last week where the group took credit for rallying hackers to take down state government sites.

Officials suspect the attacks have been prompted by anti-U.S. sentiment for the country’s involvement in the ongoing war in Ukraine.