This time, the letters are going to an undisclosed number of employees whose personal information was contained in a computer and a hard disk stolen from the trunk of a locked vehicle belonging to an employee of an auditing firm retained by Wells Fargo.

Julia Tunis, a bank spokeswoman, did not say when the equipment was stolen. But she said the bank had started sending out letters to all the affected employees yesterday.

The compromised information included names, Social Security numbers and in some cases information relating to prescription drug and health insurance claims made in 2005. The drug information included only the cost of the drugs and the dates of purchase, while the health care information only included details such as provider names and dates of service, Tunis said.

The auditing company had been hired by Wells Fargo to review the company's health plan information as required by Internal Revenue Service regulations, the spokeswoman said.

"We require all vendors and service providers to take strict measures and follow specific guidelines" for protecting sensitive data, Tunnis said. "In this case, they did not adhere to the specified policies."