Official photos of Prince William's life as a rescue helicopter pilot set off a royal alert when it was realised some of the pictures included "sensitive information".
The shots were published on the prince's official website but several were hastily recalled when it was noticed they included Ministry of Defence user names, passwords and computer screens.
The pictures, showing a day in the prince's life as a rescue pilot, had not been cleared by the ministry before being published.
They were later re-published with the sensitive details pixelated.
Defence officials spotted the mistake four hours after the photos were first published, but by then the pictures had appeared on websites around the world as well as being broadcast on television and printed in newspapers, the Daily Mail reported.
An RAF spokesman said the photographs had not been properly cleared, due to an "administrative oversight".
"The passwords and user names shown have now been reset as a precaution and we are satisfied the images do not contravene security regulations," The Sun quoted him saying.
The pictures show a day of Prince William's life as an on-call RAF search and rescue Sea King helicopter pilot at RAF Valley on Anglesey, north Wales.
The photographs are on the Duke and Duchess of Cambridge's new website, which will promote the public life of William and Catherine. It is seen as another indication of the couple's growing role as they on more royal duties.