Hackers may have stolen customers’ credit card information from the company owned by leading Republican presidential candidate Donald Trump, reports Brian Krebs, an independent cybersecurity reporter on his website Krebs on Security.

Payment cards used by customers of the hotel chain have experienced a spate of fraudulent activity, indicating a potential security breach, Krebs reports, citing three unnamed sources in the financial industry who said they had detected the fraud. The cards had been used at several properties—including the Trump International New York, the Trump Hotel Waikiki in Honolulu, and the Trump International Hotel & Tower in Toronto—over the past couple of months, they said.

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The hotel chain confirmed an earlier data breach in the fall after investigating the intrusion in July 2015. Other hotels have faced recent data breaches as well, including Hilton (HLT), Hyatt (H), and Starwood (HOT).

Trump Hotels did not immediately respond to Fortune’s request for comment. “We are in the midst of a thorough investigation on this matter,” the company told Krebs in a statement. “We are committed to safeguarding all guests’ personal information and will continue to do so vigilantly.”

Last month hackers from the hacking group Anonymous declared “total war” on Trump, the presidential candidate. But the possible data breach targeting his hotels is unlikely to be related, since it seems to have taken place months before the hackers’ scheduled attack date of April 1, and since it appears to have been motivated by financial gain rather than by activism.