The San Francisco-based bank on Friday posted a statement on its Web site saying that a computer belonging to its mortgage group had been reported as missing while being transported between Wells Fargo facilities by a global express shipping company.

The stolen system contained information such as names, addresses, Social Security numbers and mortgage loan account numbers of Wells Fargo customers. "The computer has two layers of security, making it difficult to access the information," the bank said.

So far, at least, there is no indication that the information kept on the computer has been misused in any way, said Alejandro Hernandez, a company spokesman.

Wells Fargo has begun sending letters to affected individuals informing them of the incident and advising them what they can do to mitigate any exposure to identity theft. The company will also pay for a one-year subscription to a credit monitoring service for affected individuals.

Hernandez did not disclose how many customers were affected by the breach. Nor did he say when the theft might have occurred, citing an ongoing criminal investigation by law enforcement authorities.