An NHS trust has apologised after a health worker lost a memory stick containing the information of more than 6,000 patients in a Lancashire prison.
Central Lancashire Primary Care Trust said that personal details of 6,360 prisoners at HMP Preston who have been treated by local health workers since 2000 were on the USB stick.
A spokesman for the trust apologised for the data loss, which happened on 30 December, and added that a member of staff is being investigated.
He said: "We are taking this very seriously, and we would like to apologise unreservedly for any concern this incident has caused. It should never have happened."
All USB memory sticks that are being used by health staff in the area have been withdrawn in light of the loss.
The USB stick was encrypted, and was used to routinely back up databases at the prison, but the password was written on a note and attached to it. Details on the stick included prisoners' ailments, but no full medical histories.