Cardiff prison wrongly sent inmates' details
22 October 2013 Last updated at 10:04 BST
The Ministry of Justice has been fined £140,000 by the Information Commissioner's Office after details of more than 1,000 inmates at Cardiff prison were emailed to three prisoners' families.
Prisoners' names, ethnicity, addresses, release dates and offending history were among the data sent out.
The breaches were only discovered when the third recipient alerted the prison to the fact they had received a file.
The ministry said the prison had now altered its procedures since the incidents in August 2011.
Anne Jones, the assistant information commissioner for Wales, spoke to BBC Radio Wales' Felicity Evans about the case.