"I saw, well, what's this? I don't buy ladies clothing. I didn't go to Home Depot. I don't have a Sprint account," Yu said.
He saw a check with his number on it, but somebody else's signature.
"I couldn't believe it," Yu said. "I thought it was a processing error."
The problem: his Bank of America account number recently belonged to somebody else.
"Eventually I discovered that B of A recycles checking account numbers," he said
Bank of America wouldn't comment on camera but did confirm that when an account is closed its number may be reused. Other banks do the same. Industry officials say the banks are running out of numbers.
"As the number of checking accounts increases we will see the use or the reuse of those checking account numbers increase as well," said Peter Soraparu, executive director of backing industry group BAI.
But do the math: there seem to be plenty of numbers available.
"If we had nine digit numbers, there would be 10 to the 9th equals one billion possibilities," says math professor David Meredith of San Francisco State University.
However, Meredith explains, account numbers are actually like secret codes and that greatly limits the numbers banks can use. So they have to throw out a lot of numbers to make sure the numbers are secure in some sense.
Banks advise consumers to do what Dennis Yu did: review your account often. But account number recycling still leaves plenty of room for confusion.
Finally, consider the plight of the San Francisco man whose says his account was frozen because the bank told him he was dead. He got his money only when the bank concluded the deceased was the previous holder of his recycled account number