Tax forms mailed out by your bank contain all sorts of information you probably don’t want to land in the hands of a random stranger: Name, address, partial Social Security number, account number, and more. Yet, one large bank screwed up and sent this sensitive information to the wrong customers.

The Chicago Tribune reports that BMO Harris — which operates more than 600 branches in eight states — is working to determine how the processing error occurred after customers began receiving someone else’s tax-related mailings.

The particular document involved in this mix up is IRS Form 5498, which includes details on a customer’s annual contributions to their individual retirement account.

Customers tell the Tribune that the forms they received looked as if they were supposed to be cut into two pieces with each piece going to a different person.

For now, BMO Harris is unsure how many customers were affected by the issue.

“The safeguarding of customer information is of paramount importance to us and we are currently (assessing) the issue to determine the cause,” a rep for the company tells the Tribune.

The company says it will mail apology letters and new tax forms to affected customers, and advises them to keep an eye on their credit reports.

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