A cyber attack caused printing and delivery disruptions on Saturday at the Los Angeles Times and other major U.S. newspapers, including ones owned by Tribune Publishing Co such as the Chicago Tribune and Baltimore Sun.

The attack appeared to originate outside the United States, the Los Angeles Times reported, citing a source with knowledge of the situation.

The attack led to distribution delays in the Saturday edition of The Times, Tribune, Sun and other newspapers that share a production platform in Los Angeles, the Los Angeles Times reported.

Tribune Publishing, whose newspapers also include the New York Daily News and Orlando Sentinel, said it first detected the malware on Friday.

The West Coast editions of the Wall Street Journal and New York Times were hit as they are also printed on the shared production platform, the Los Angeles Times said.

Tribune Publishing said the virus hurt back-office systems used to publish and produce “newspapers across our properties.” It added that the print edition of the Chicago Tribune was published Saturday without paid death notices and classified ads, while in other markets a similarly slimmed-down version of the Saturday newspaper would be delivered on Sunday.

“We are aware of reports of a potential cyber incident affecting several news outlets, and are working with our government and industry partners to better understand the situation,” the Department of Homeland Security said.