Broadband provider Demon Internet has come forward and admitted leaking the personal details of some of its customers.
The company mistakenly sent out a spreadsheet containing over 3,600 email addresses, telephone numbers and usernames for its e-billing system to several of its subscribers.
According to PC Pro, details about government officials, NHS trusts and police are included on the document.
Talking to the website, Demon Internet said the spreadsheet does not include any financial information.
It added: "We would like to apologise to all concerned but state that this was a limited and isolated case caused by human error and to reassure customers that their security is our key priority."
Demon Internet was founded in 1992 and offers range of services, including shared web hosting, national Ethernet, virtual private networks and leased lines.
The company was bought by THUS in 1998.