An unusual cyberattack disrupted printing operations at newspapers in Los Angeles, San Diego and Florida on Saturday, and the Los Angeles Times said it had come from outside the United States.

Computer malware attacks on infrastructure, while relatively rare, are hardly new. But this would be the first known attack on major newspaper printing operations, and if politically motivated, it would define new territory in recent attacks on the media.

The malware was focused on the networks used by the Tribune Co., which until recently owned the Los Angeles Times and the San Diego Union-Tribune. Both papers still share their former parent company’s printing networks.

The Los Angeles Times said the attack also affected the distribution of the New York Times and the Wall Street Journal, which share use of a large printing plant in Los Angeles for their West Coast editions. Both appear to have been collateral damage; there was no evidence that they were hit by the same malware aimed at the Tribune company.

The online editions of the news organizations were not affected, and Tribune Publishing said no data about its subscribers was compromised.

“Every market across the company was impacted,” Marisa Kollias, a spokeswoman for Tribune Publishing, told the Los Angeles Times. The Tribune’s remaining publications include its flagship, the Chicago Tribune, and newspapers in Florida, Hartford, Connecticut, and Maryland. It also owns the Daily News in New York.

Missing from Tribune’s statements were any details about the nature of the malware or evidence for its assertion that the attack originated overseas. Anonymous sources cited by the Los Angeles Times suggested that the malware may have been a form of ransomware — a pernicious attack that scrambles computer programs and files before demanding that the victim pay a ransom to unscramble them.

Even if the attack was the work of foreign hackers, that does not necessarily mean it was backed by a government.

Neither the Tribune Co. nor the Los Angeles Times said the attack was linked to a ransom demand.

Today, Hillary Manning, vice president of communications for the Los Angeles Times, said, “The presses ran on schedule, and papers were being delivered as usual today.”