The attack came from a "foreign entity" aiming to "disable infrastructure, more specifically servers", rather than steal the data, the paper's source explained.
According to Light, the virus impacted computer systems of Tribune Publishing Co. that are still shared by the U-T and the Los Angeles Times, which were purchased by Los Angeles billionaire Dr. Patrick Soon-Shiong in June but haven't yet transitioned from the old systems.
"We apologize to our customers for this inconvenience".
"There is no evidence that customer credit card information or personally identifiable information has been compromised", Dearborn wrote.
While the Times noted it was aware of the problem on Friday, its technology teams attempted to fix it, but couldn't resolve the matter before production was set to begin. As a result, several Saturday newspapers will be distributed in their slimmed-down versions on Sunday.
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Readers can access a digital edition of the Saturday paper here. Under an ongoing transition agreement, Tribune Publishing, formerly known as Tronc, continues to print the two West Coast newspapers and provide other essential services. The West Coast editions of the two NY papers are printed at the same Los Angeles printing facility as the L.A. Times.
Even though the Union-Tribune is no longer owned by Tribune Publishing, Light said it is "still transitioning away from the Tribune systems". At The Baltimore Sun, for example, the usual comics and puzzles were not included in Saturday's print edition, the paper tweeted.
"The malware unfortunately impacted our timeliness and delivery of Saturday's Chicago Sun-Times", Kollias said.
And staffers at some of the affected papers said they haven't received much information from management about the extent of the cyberattack.
Malware has, over time, become more sophisticated and coordinated, involving more planning by networks of hackers who infiltrate a system over time, she said.