Sensitive case notes on vulnerable children in Essex have been found on a computer sold on eBay's auction site.
Files about vulnerable children were on an e-Bay computer
Reports and details about fostering and adoption were found among 1,000 files on a £1.70 computer previously owned by Southend Borough Council.
The buyer, from Staines, Surrey, has asked to remain anonymous but told the BBC it was a serious lapse of security.
Paul Greenhalgh, from Southend council, said a recycling contract was under review and an inquiry was under way.
The eBay customer said he feared the information could have got into the hands of people who prey on children.
He said: "It was as bad as it could be it, everything was about vulnerable children in Southend.
"It was a sort of snap shot of documents from meetings to decide whether or not a child would go to a special school, details of whether they'd been physically or sexually abused.
"It went on and on. I was absolutely horrified."
Documents included fostering, child protection, placement plans and adoption records between 1999 and 2003.
The council said it handed the computer, along with 19 others containing the same information, to the Revitalise recycling company at Maldon in Essex.
Mr Greenhalgh said: "We are making sure that we are cleaning all our computers before we dispose of them in-house rather than using an external contractor to do that for us."
Jon Dixon, of Revitalise, said: "We're trying our best to find out exactly what happened.
"We're reviewing our policies and procedures because we have quite robust procedures which is why we are struggling to understand really what's gone wrong."
Surrey Police now have the computer and Southend Borough Council has set up a helpline on 01702 215983.