Fidelity Investments has said a laptop containing sensitive data on roughly 196,000 retirement account customers was stolen last week, the firm says.
The computer has details about Hewlett Packard pensioners
The US's largest mutual-fund manager has confirmed that the computer held information on participants in Hewlett-Packard's pension plan.
It has offered those affected a year's free credit monitoring.
Data on the computer, stolen earlier in March, includes names, addresses, birth dates, and social security numbers.
However, Fidelity said there was no evidence the data had been misused. It would not say where the theft took place, but said it was not taken from a Fidelity or a Hewlett-Packard building.
Boston-based Fidelity is working with police and the computer maker to find out who stole the laptop.
It also said it would reimburse account holders for any losses linked to unauthorised transactions connected to the stolen laptop.
So far, Fidelity said, it had not noticed any unusual movement in the affected accounts.
And it revealed that a software application that would allow someone to read the personal data had expired.
This, said a spokesman, would make it very difficult to access the information, adding that personal identification numbers were not on the computer.