LONDON — A disk which a tabloid said carries personal details on some 100,000 serving British military personnel is missing, the Ministry of Defense said Friday.

The military acknowledged a report in The Sun newspaper that contractor EDS lost track of a portable hard drive, but said it could not comment on the claim that it contained names, addresses, passport numbers and driver's license information of service personnel along with data on 600,000 potential recruits.

"We don't know what's on it, and we don't even know if there's anything on it," a ministry of defense spokesman said, speaking anonymously in line with military policy.

A government mandated data security review was unable to account for the disk, according to EDS UK, the British subsidiary of Plano, Texas-based EDS. It said the disk was being stored at its secure facility in Hook, a town about 45 miles west of London when it went missing.

EDS refused to say whether the disk was encrypted.

The military said it was investigating the incident, which it said became known earlier this week.

The loss is one in a series of information breaches at the ministry. Last month it said a disk carrying sensitive personnel information was stolen from a military base. Earlier this year the military said a laptop with details of 600,000 new and prospective recruits was stolen.

The British government has struggled to get a handle on data losses even as it rolls out an ambitious national identification card program. Last year's loss of computer disks containing information _ including banking records _ on nearly half the U.K. population caught international attention, and a steady stream of data blunders since then has kept the spotlight on the way the government stores and handles data.

EDS, an information technology company, has worked on a range of British government projects, including providing support for its pensions department, the ministry of justice's offender management system, and a major contract to upgrade the military's IT infrastructure, according to the company's Web site.

EDS was bought by computer maker Hewlett-Packard Co. earlier this year.