The Ministry of Justice is to be fined £140,000 by the data watchdog after the personal details of all 1,182 prisoners at a jail were mistakenly emailed to inmates' families.
A spreadsheet containing sensitive information including names, ethnicity, addresses, sentence length, release dates and details of the offences by all inmates at HMP Cardiff was sent to three families, the Information Commissioner's Office (ICO) said.
The breach was only discovered when one of the recipients contacted the prison on August 2, 2011 to report they had received an email from the prison clerk about an upcoming visit, which included the file.
The ICO found there was a clear lack of management oversight at the prison, with the clerk working unsupervised despite only having worked at the prison for two months and having limited experience and training.
More top news
The extent of last winter's floods has been revealed after a survey by the Local Government Association
Jackie Walker, vice-chair of the pro-Corbyn group Momentum, was suspended over comments shown on a leaked video.
Britain's biggest auto company Jaguar Land Rover said some European customers are turning their noses up at UK-made vehicles.