The UK arm of insurance giant Zurich has lost a back-up tape containing the personal data of around 51,000 customers.
Zurich says the back-up tape - which in some cases contained contact information and bank details - was lost during a routine transfer within South Africa to a data storage centre in August 2008. Some details of customers in South Africa and Botswana were also on the tape.
The firm says it has written to the general insurance customers but that there is no evidence that the data has been misused by fraudsters.
In addition, it has appointed KPMG to investigate the loss, with the accountancy firm also advising on moves to strengthen security procedures. Zurich UK has also "taken steps" to improve transportation security of data tapes.
The Financial Services Authority and UK Information Commissioner's Office have also been informed.
Annette Court, CEO, Europe general insurance, Europe, Zurich, says: "We are implementing the necessary steps to minimise the impact of this situation on our customers. Protecting our customers' interest is at the top of our agenda. We are putting a great deal of investment into strengthening our internal processes to ensure that incidents of this nature do not happen again in the future."