The theft only affect customers with a personal line of credit with the bank, said Alejandro Hernandez, a company spokesman. It doesn't affect customers who have deposit accounts, he said.
The information stolen from the office in the San Francisco area includes names, addresses, Social Security numbers and account numbers. It's unknown whether whoever took the information knows that they have it, Hernandez said.
So far, there is no evidence the information has been misused, he said.
Wells Fargo declined to say how many customer were affected, but described the number as a small percentage of its customers.
The company said it has taken steps to protect customers from fraud, including giving customers new accounts, alerting credit reporting agencies of the theft, and hiring a company to watch for any unusual activity on the accounts.
"Should there be any misuse, we'll fully shield the customer from financial liability," Hernandez said.
The San Francisco-based company also urged customers to request a fraud alert with one of the three national credit reporting agencies to protect themselves against identify theft.