Patrons of the Graton Casino and Resort may have lost more than just their money as the business has started notifying customers that some of their personally identifiable information may have been compromised.

The casino, located in Rohnert Park, Calif., is citing a human error for a mistake that saw a company employee mistakenly include customer information, such as, addresses and Social Security numbers in an attachment that was sent along with an undisclosed number emails between February and August 2017, The Press Democrat reported. The problem was discovered on Sept. 1.

Casino officials told The Press Democrat that after it “discovered that certain personal information was inadvertently distributed in a small number of email attachments as ‘hidden' information that could be revealed via certain manipulation by the recipients.”

The Graton Casino would not reveal how many people are potentially affected.