More than 1,000 victims of crime have accidentally had their email addresses shared with other victims of crime after a mistake by the Metropolitan Police.
The "human error" occurred after their details were inserted in the wrong box of an email sent by the Met to distribute a quality control survey.
It was sent to 1,136 people in seven batches, meaning the email addresses of those affected were seen by up to 197 other people.
A Scotland Yard spokesman said: "No other personal details were revealed and we are contacting everyone affected to explain what happened and to apologise."
The Met said it was reviewing how it carries out surveys to avoid similar mistakes being made in the future.
Nick Pickles, director of privacy group Big Brother Watch, said: "The fact that technology makes it easier to make mistakes does not excuse the mistakes.
"Given how much personal information is now collected and held, it is time for the sanctions to be far greater and real action taken to protect people's privacy."
The Information Commissioner's Office said: "We have recently been informed of a possible data breach which may involve the Metropolitan Police.
"We will be making inquiries into the circumstances of the alleged breach of the Data Protection Act before deciding what action, if any, needs to be taken."