Private data has been lost by or stolen from UK local councils more than 1,000 times since 2008, a report says.
The data included details relating to children and vulnerable people in care, campaign group Big Brother Watch said.
Some 132 authorities said they had had a total of 1,035 cases of data loss or theft between 2008 and 2011.
The Information Commissioner said it was vital councils kept data secure. The Local Government Association for England and Wales declined to comment.
Big Brother Watch director Nick Pickles said the research - based on answers to freedom of information requests - showed a "shockingly lax attitude" to protection of confidential information by some councils.
Some 263 councils reported no losses, while a further 38 did not respond.
The report revealed that information about at least 3,100 children and young people was compromised in 118 cases.