Zurich Insurance has admitted losing the personal account details for more than half a million people more than a year ago.
The details of 51,000 British customers were on the tape, along with hundreds of thousands of details from people in South Africa and Botswana. They should have received letters warning them of the loss in recent days.
The data was backed up on tape and was on its way to a South African storage centre when it was lost in August 2008. It included account details for 51, 000 British customers, 550, 000 South African customers and about 40, 000 accounts from Botswana. The insurer said it had seen no evidence that the information was being used for ID fraud or otherwise exploited.
Customers at risk are those with Zurich general insurance, not life insurance.
Zurich has hired KPMG to sort out its data protection policies and has also kept the Financial Services Authority and the Information Commissioner's Office informed.
A spokeswoman for Zurich told the Register: "People have been calling the phonelines for reassurance and generally the response has not been bad. We've hired KPMG to find out why it has taken so long for this loss to come to light."
Annette Court, chief exec of Zurich UK, apologised for the loss and said the firm was improving internal procedures to "ensure that incidents of this nature do not happen again.".
There is a dedicated phoneline number included in customers' letters or you can call 08000 152 183 from the UK or +44 1709 764 401 from outside the UK. There is also information at http://www.zurich.co.uk/home/aboutus/id.htm