The computer was in Fidelity's possession, which is administering a retirement program for HP employees.
Fidelity has sent email or letter notifications of the incident to all affected HP employees, said Anne Crowley, Fidelity spokeswoman.
"The personal information was encoded on the laptop," she said. "(The code license for) that information expired the day after the theft."
Crowley did not reveal where the incident took place, other than it was somewhere within the U.S., because local authorities are investigating the theft. Fidelity has not been notified of any misuse of the affected information.
HP said in a statement that it is working closely with Fidelity to "minimize the impact" of the information breach.