The Department of Health has apologised for a "very serious" security breach at a jobs website for junior doctors.
Channel 4 News revealed details of the problem, which saw personal details of job applicants made publicly available online.
The information includes addresses and telephone numbers, details of previous convictions and sexual orientation and religion.
There had already been complaints that a new computerised system for selecting candidates for specialist training were unfair on those applying for jobs.
The latest security breach is set to further damage confidence in the process, and has prompted an apology from the Department of Health.
"We apologise to any applicants whose details have been improperly accessed. This is a very serious matter and is under investigation," said a spokesman.
"This URL was made available to a strictly limited number of people making checks as part of the employment process.
"This information was never publicly available through the NHS Medical Training Application Service website and was only accessible for only a short period of time after details of the URL were leaked.
"The MTAS team fixed the problem as soon as it was brought to their attention."
And health minister Lord Hunt told BBC Radio 4's Today programme that the "security breach and leak is very serious indeed".
"It's quite clear that it was leaked. We need to find out the full information, but clearly very few people had access to this data. It has been made available to the media," he added.
"It's so serious that we have this thorough investigation taking place at the moment."
Conservative health spokesman Damian Green said: "This is yet another insult to junior doctors."
