Customer data has been stolen from Ashley Madison, a dating website for married people who wish to have an affair.
The hackers claim that they have obtained information including "all the customers" secret sexual fantasies and matching credit card transactions".
The hackers name themselves the Impact Team, and have said that they managed to steal the real names and addresses of the site's users, including those who had previously paid to "delete" their accounts.
People could hide their profiles for free, but the website charged them $19 for a full delete. According to the hackers this was a big lie as personal information was still kept on their systems.