"It was down to human error. Procedures were not followed fully and we have learned from it," Barclaycard told the BBC.
"All Barclays customers have a 100 per cent fraud guarantee as long as they take reasonable care of their information."
The bank has introduced a new security code word system for senior employees so that the same incident could not happen again.
Experts have already warned that 2008 will be a bumper year for identity fraudsters.