In the latest example of the growing cyber threat to critical infrastructure, Cleveland Hopkins International Airport was hit by a ransomware attack last week. The ransomware disrupted the airport’s systems used for email, payroll and digital records. In addition, most screens around the airport that are used for digital signage became unavailable.

The office of the Mayor of Cleveland, Ohio described the attack, which is being investigated by the FBI, as “an isolated technical incident.” Critical operations at the airport were not affected, so security screening continued without issues and no flights were delayed.

Read more: Ransomware Hits Yet Another U.S. Airport