The websites for some major U.S. airports went down early Monday in an apparent coordinated denial-of-service attack, although officials said flights were not affected.
The attacks followed a call by a shadowy group of pro-Russian hackers that calls itself Killnet for coordinated denial-of-service attacks on the targets. The group published a target list on its Telegram channel.
Security experts said that this type of attack is highly visible but not as dangerous as other forms of hacking.
"We noticed this morning that the external website was down, and our IT and security people are in the process of investigating," said Andrew Gobeil, a spokesman for Atlanta's Hartsfield-Jackson International Airport. "There has been no impact on operations."
Portions of the public-facing side of the Los Angeles International Airport website were also disrupted, spokeswoman Victoria Spilabotte said. "No internal airport systems were compromised and there were no operational disruptions."
Spilabotte said the airport notified the FBI and the Transportation Security Administration, and the airport's information-technology team was working to restore all services and investigate the cause.
Several other airports that were included on Killnet's target list reported problems with their websites.
The Chicago Department of Aviation said in a statement that websites for O'Hare International and Midway airports went offline early Monday but that no airport operations were affected.
Last week, the same group of hackers claimed responsibility for cyberattacks against state government websites in several states.
John Hultquist, vice president for threat intelligence at the cybersecurity firm Mandiant, tweeted that denial-of-service attacks like those aimed at the airports and state governments are usually short in duration and "typically superficial."
"These are not the serious impacts that have kept us awake," he said.