The US TV station operator Sinclair Broadcast Group said on Monday it had found some of its servers and workstations had been encrypted with ransomware, disrupting office networks.
Sinclair said it was investigating what information the ransomware affected and had notified law enforcement and other governmental agencies.
Ransom software works by encrypting victims' data and can include locking down a company's network or stealing data. Typically hackers will offer the victim a key in return for cryptocurrency payments that can run into hundreds of thousands or even millions of dollars.
Colonial Pipeline suffered a crippling cyberattack earlier this year that disrupted fuel supplies for almost a week, leaving thousands of gas stations in the U.S. Southeast without fuel.
Sinclair, the second-largest U.S. TV station operator, said the ransomware attack may disrupt advertisements by its local broadcast stations and that the company cannot currently determine whether it will have a material impact on its business or financial results.