A council has apologised and referred itself to the Information Commissioner after it published the personal data of 100 people with special educational needs (SEND).
Central Bedfordshire Council said the data was accidentally published after a Freedom of Information Act request about schooling was released on Monday afternoon.
The information has since been removed from the website.
The Central Bedfordshire SEND action group called the mistake "catastrophic" but said it was "unsurprising".
It said the breach was of particular concern for fostered and adopted children who may have appeared on the list.
In a statement the group said: "It is the latest in a long history of incompetence and disregard for the law in relation to SEND families.
"This catastrophic mistake poses a particular safeguarding risk to fostered and adopted children and demonstrates the ongoing culture of negligence toward SEND children that has been ingrained at CBC for at least a decade."
Central Bedfordshire Council said it took its responsibility of looking after people’s personal data "extremely seriously" and employees received regular training and reminders about protecting personal and sensitive information.
In a statement, a council spokesperson, said: "Regrettably we were made aware of data being accidentally released to a public website on Monday afternoon, but our officers worked swiftly to get the information removed.
"We are extremely sorry to all of those affected and we are in the process of contacting all of the families affected to apologise directly."
It added that it had already made changes to its procedures since the data breach would work on any recommendations that were made by the Information Commissioner.
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