"We believe the intention of the attack was to disable infrastructure, more specifically servers, as opposed to looking to steal information", the source said, adding the attacker was a "foreign entity".
A cyber-attack has caused printing and delivery disruptions to major United States newspapers, including the Los Angeles Times, the Chicago Tribune and the Baltimore Sun.
"There is no evidence that customer credit card information or personally identifiable information has been compromised", she said.
On its Twitter account, Tribune Publishing Company acknowledged the issues, empathizing with customers affected.More news: GOP and Democrats trade blame for shutdown, no deal in sight
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Jeff Light, the editor and publisher of the San Diego Union-Tribune, said in statement the attack appeared to begin Thursday night and continued into Friday for their production. For print subscribers that did not receive Saturday's paper, they will receive the paper with their regularly scheduled delivery of the Sunday edition.
The issues also affected distribution of the San Diego Union-Tribune as well as editions of the Wall Street Journal and New York Times, which are all printed at the Los Angeles Times' Olympic Printing Plant in downtown Los Angeles.
Tribune Publishing spokeswoman Marisa Kollias said the virus hurt back-office systems used to publish and produce "newspapers across our properties". "We are doing everything we can to restore full service and to continue to make our journalism available to you both in print and digitally", Light's statement read.
Light said the digital replica of the paper was also affected.
Saturday editions of suburban Chicago newspapers the Lake County News-Sun and Post-Tribune will also be among those to be delivered on Sunday.