We’ve told you before about Comcast not really paying attention to the payments it receives — like the woman who accidentally sent them her rent check and found that it had been deposited in the cable company’s account — but here’s a story of a man who isn’t even a Comcast customer but found that $500 had been taken out of his bank account anyway.

The man tells the Cleveland Plain Dealer that not only isn’t he a Comcast subscriber, but the cable giant doesn’t serve his area.

But there it was on his bank statement: $500 paid to Comcast.

His bank, Huntington, didn’t appear to give him too much of a hassle, crediting the money to his account after he filled out the proper documents. But how did this happen?

The bank pinned the blame on an “incorrect keystroke,” but as the Plain Dealer’s Teresa Dixon Murray notes it could also be fraud.

All one needs to process an electronic bank-to-bank check (aka an “Automated Clearing House” or ACH payment) is the bank account number, and the account’s relevant bank routing number. This information is available on your standard printed check, so anyone who gets their hands on an old check has everything they need.

“They don’t need your name or address or ZIP code or anything else,” writes Dixon Murray. “So if someone wants to pay for something online or by phone with an ACH… he or she could pick a bank and find its routing number, which is easy. And then pick an account number with the correct number of digits. Gold!”

ACH transactions are monitored by NACHA — The Electronic Payments Association — but that’s no guarantee that errors and fraud won’t happen.

Someone fraudulently using another person’s account info for ACH transactions will likely be caught in the long, but only if the victim spots the bogus transactions. As the man in this story noted, if he hadn’t caught the questionable statement entries himself, his accountant probably would have assumed it was a legitimate purchases.

“My accountant would have no idea whether Comcast was my internet provider and, if I had not checked, it would have been written off as a business expense,” he explains.

The best you can do is to be careful about not sharing your account info — Dixon Murray even suggests having a smaller, secondary checking account for writing checks to people or businesses you don’t necessarily trust — and to remain vigilant about checking your accounts for signs of potential errors or fraud.

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