Britain's biggest police force apologised on Thursday to more than 1,100 victims of crime after admitting it had "inadvertently" shared their email addresses with other victims.
London's Metropolitan Police was emailing out a survey about the service it provides when the blunder occurred on Monday.
"In total 1,136 emails were sent out in seven batches of between 119 and 198 recipients, but because the addresses were put in the wrong box they were visible to the other recipients in the batch," the Met said in a statement.
"No other personal details were revealed and we are contacting everyone affected to explain what happened and to apologise."
The force blamed human error and said it was reviewing the way it conducted surveys to "minimise the risk of similar mistakes being made in the future".
The Information Commissioner's Office, which upholds information rights including data privacy, had been informed, the statement added.