A study of 200 hard drives bought on eBay this year reveals that over 70 per cent contained sensitive personal or business data.

German data recovery firm O&O Software was able to recover 3.3 million files, including 40,000 Word documents, 15,000 Excel spreadsheets and about 50 complete email inboxes.

In one case a large German bank left details of customer credit ratings in files which O&O said were only protected by being labelled 'Highly Confidential'.

"The most interesting documents of all came from a former managing director of a middle-sized company who meticulously recorded every aspect of his discord with the other managing directors," said Olaf Kehrer of O&O in the report.

"Starting with normal mail correspondence concerning blame, all the way to accusations of fraud and embezzlement with specific shareholders, one could very easily trace the path of this company to probable bankruptcy.

"All in all, this was extremely explosive material that should never have made it into the public domain."

However, there were some encouraging findings in the study. The number of drives bought that had been securely reformatted doubled from last year's figure, although the proportion of drives bought that proved faulty was also higher.

The report also mentions finding what it calls 'onion drives'. These are drives that have been formatted by users and still left with data written onto the hard drive.