Business publications owned by Rupert Murdoch’s News Corp., including the Wall Street Journal and Barron’s, have found evidence of hacking to their systems going as far as 2012, the company warned Friday.

Company officials said that the breach was “likely part of a broader campaign involving a number of other victim companies.”

In a letter to customers Friday, William Lewis, CEO of News Corp.’s Dow Jones unit, warned of “unauthorized access to our systems” between August 2012 and July 2015 that may have affected as few as 3,500 credit cards.

Dow Jones runs the Wall Street Journal, Barron’s and online financial publication MarketWatch.

Lewis’ letter, a copy of which was obtained by USA TODAY, said there was no evidence any information has been stolen. But the focus of the attack appears to have been to obtain “contact information such as names, addresses, email addresses and phone numbers of current and former subscribers in order to send fraudulent solicitations,” the CEO warned.

“Out of an abundance of caution, we are notifying you that we recently determined there was unauthorized access to our systems,” the letter said. “To date, our extensive review has not uncovered any direct evidence that information was stolen, and we have taken steps to stop the unauthorized access.”

Lewis said the law enforcement recently warned of the breach, and that the company has been investigating the problem internally since late July. He said the company is working with law enforcement and warned that other companies may also have been targeted.

“We understand that this incident was likely part of a broader campaign involving a number of other victim companies,” the letter said.

The Wall Street Journal and its weekly sister publication Barron’s are well read by financial professionals, including by Wall Street traders and brokerage houses. Murdoch is executive chairman of News Corp. along with his son Lachlan.

Follow USA TODAY business reporter Kaja Whitehouse on Twitter @kajawhitehouse

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