More than half of employees have accidentally sent a sensitive email to the wrong address, according to research by Sophos.

And more than two thirds of businesses are seriously concerned about data leakage via email.

The risk is a serious one, said Graham Cluley, senior technology consultant at Sophos.

"As more and more business, and indeed personal interaction, is conducted via work email, the risk of slipping up and clicking send without double-checking the recipient's details is ever-growing," said Cluley.

Four of the largest Internet Service Providers in the US now offer a service that charges businesses for guaranteed delivery of their emails to the correct address.