Hacking attack appeared to originate outside the US, experts said, but it was unclear if a state actor was involved.

A cyber attack caused major printing and delivery disruptions on Saturday at the Los Angeles Times and other major US newspapers, including ones owned by the Tribune Publishing Co.

The cyber 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 and reported it to the FBI.

However, Tribune Publishing’s website was not affected and no customer information was compromised, according to the statement issued by the company on Saturday.

“This issue has affected the timeliness and in some cases, the completeness of our printed newspaper,” Tribune Publishing spokesperson Marisa Kollias said in a statement. “Our websites and mobile applications, however, have not been impacted.”

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

The LA Times said Saturday that the attack, which was first assumed to have been a server outage, hit a computer network at Tribune Publishing which is connected to the production and printing process of multiple newspapers around the country.

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The report said it could not provide firm numbers on how many subscribers were impacted, but a majority of LA Times customers received their papers on Saturday morning, albeit several hours late.

Most San Diego Union-Tribune subscribers were without a newspaper on Saturday as the virus infected the company’s business systems and hobbled its ability to publish, the paper’s editor and publisher Jeff Light wrote on its website.

“We believe the intention of the attack was to disable infrastructure, more specifically servers, as opposed to looking to steal information,” the LA Times quoted a source with knowledge of the situation as saying.

The paper cited officials as saying it was too soon to know whether it was carried out by state or non-state actors.

A spokesperson for the Department of Homeland Security said it was studying the situation. “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,” Katie Waldman said in a statement.

An internal memo from Tribune’s CEO Justin Dearborn on Saturday referenced “malware” and said, “we are making progress with this issue”.