Unisys has put up a $50,000 reward for information leading to the recovery of a desktop PC which contains personal information on 38,000 people, 18,000 of whom are military veterans.
The PC was first listed as missing from Unisys' offices in Virginia on 3 August. It contains details of patients treated at medical facilities in Philadelphia and Pittsburgh run by the US Department of Veterans Affairs (DVA).
The information may include patients' names, addresses, social security numbers, dates of birth and military service and insurers, billing and claims information.
Unisys was in possession of the information because it is contracted to the DVA to collect medical insurance data.
The DVA's inspector general, the FBI and local law-enforcement agencies are conducting a "thorough investigation" of this matter, Secretary of Veterans Affairs R James Nicholson said in a statement.
As well as posting the reward, Unisys is helping the FBI with its enquiries.
Two days after the Unisys PC went missing, police in Maryland arrested two 19 year-olds and a minor for the theft of an HP Pavilion laptop and external hard drive that also contained information from the DVA.
The laptop and hard drive, containing personal and financial information on more than 25 million veterans, active-duty military personnel and their spouses, was stolen in a burglary on 3 May.
Facebook database included text-message metadata - despite not using Facebook Messenger for SMS
Successful attack could result in harm to patients and financial loss, warns NHS governing body