Several major US newspapers are kicking off 2019 responding to a cyberattack that caused print and delivery problems for publications owned by Tribune Publishing, including the Chicago Tribune and Baltimore Sun, as well as the Los Angeles Times.

Few details are still known about the attack, which hit printing plants in Los Angeles and various Tribune Publishing papers across the country, the Associated Press reports. The incident caused delays for some publications; others were forced to cut certain portions of content.

"This issue has affected the timeliness and in some cases the completeness of our printed newspapers," said Tribune Publishing spokeswoman Marisa Kollias in a statement to the AP. For example, the Chicago Tribune ran Sunday, December 30, without classifieds or paid death notices. Some papers were forced to cut content and distribute Saturday papers on Sunday instead.

In Los Angeles, the attack prevented timely delivery for the Los Angeles Times, San Diego Union Tribune, and other newspapers to certain recipients. Both the Los Angeles Times and San Diego Union Tribune were sold to Dr. Patrick Soon-Shiong in 2018; however, the New York Times reports the two publications still use their old parent company's printing networks.

It's worth noting the attack only affected printed papers, Kollias noted. Websites and mobile applications for targeted publications were not targeted by this attack.

According to a Los Angeles Times report, several people with knowledge of the attack say it appears to be "Ryuk" ransomware. An individual from the company who did not have permission to comment publicly said corrupted files had the ".ryk" extension.

Ryuk targeted several enterprises in August 2018, encrypting hundreds of machines, storage, and data centers in each. Its technical capabilities are "relatively low," Check Point Research reports, but some businesses paid big ransoms to get their files back. Analysts linked this particular Ryuk campaign, and some of its inner workings, to the Hermes ransomware — a form of malware frequently connected to the North Korean APT Lazarus Group, they explain.

Unlike common ransomware, Check Point previously said Ryuk is exclusively used for tailored attacks. "In fact, its encryption scheme is intentionally built for small-scale operations, such that only crucial assets and resources are infected in each targeted network with its infection and distribution carried out manually by the attackers," researchers write in a report on Ryuk.

Tribune Publishing has not issued a formal statement describing the threat found on its network. However, if Ryuk was the malware used here, Tribune wouldn't be the only company facing this threat. On January 2, KrebsOnSecurity reported Data Resolution, a cloud hosting provider, was bringing its systems back online after Ryuk ransomware hit on December 24, 2018.

The report states Ryuk was the same malware strain that targeted US newspapers. Following the incident, Data Resolution shared an update with affected users to say attackers compromised a login account to infect servers with Ryuk ransomware. The company, which has about 30,000 business customers around the world, says there is no sign data was stolen.

The Washington Post reports Tribune is still investigating the malware, which affected a part of its back-office systems, Kollias said in a statement. Tribune has also reported the attack to the FBI, the Chicago Tribune says. So far, Kollias said to the Chicago Tribune, there is no evidence indicating customer credit card data or personally identifiable information had been affected.

For those keeping an eye on the Tribune attack, there remain more questions than answers. We still know little about who may be behind the incident, whether they may be linked to foreign governments, what their motivations are, or how, exactly, they successfully broke in.

Tribune Publishing declined to comment for this article.

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