Senior RAF officers could be at risk of blackmail and identity fraud after the theft of hundreds of computer files that included information about extra-marital affairs and drug taking.
The information was gathered as part of routine security clearance investigations.
The Ministry of Defence (MoD) said about 500 files stored on three computer hard drives went missing from RAF Innsworth, Gloucester, last September.
A spokesman for the MoD said all those at risk have been alerted, but there is no evidence to suggest the information had been targeted by "criminal or hostile elements".
"All individuals identified as being at risk received personal one-on-one interviews to alert them to the loss of data, to discuss potential threats and to provide them with advice on mitigating action," he said.
In October last year, the MoD revealed that a hard drive lost by IT services company EDS may have contained details of 1.7 million people.
The unencrypted went missing from EDS premises in Hampshire. The drive's loss was revealed during an ongoing audit of data security ordered by the Cabinet Office.
News of the latest MoD data breach comes as the Information Commissioner's Office (ICO) said it is to review 140 breaches by the NHS in which tens of thousands of personal records were lost.
The ICO continues to step up action around data privacy, announcing last week that it has prosecuted a Peckham recruitment company and a Lewisham law firm for failing to register as data controllers.