One American man, a banker, is said to have signed up to the adultery site because he had a "sex drive too high to handle".
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Brian Krebs, the blogger who first reported the breach, said the hackers were threatening to release all Ashley Madison's customer records if the website isn't shut down.
The hackers called themselves the "Impact Team," and the potential release includes "profiles with all the customers' secret sexual fantasies and matching credit card transactions, real names and addresses, and employee documents and emails." In a statement, Avid Life Media, the parent company, said: "At this time, we have been able to secure our sites, and close the unauthorized access points.
Personal details of up to 32 million users of the site, which has the tagline "Life is short.
Have an affair", were released after it was hacked last month by a group calling itself The Impact Team.
Admitting to infidelity might still be the last thing most people would want to do in public.