The second leak is 20GB, almost twice the size of the first batch of private information - including email addresses and credit card numbers - which was released on Wednesday.
Around 37m members' details have been compromised by the hacking group Impact Team, which first revealed it had gotten hold of customer information in July.
The group followed through with threats to publish the information, and the latest dump was accompanied by a message saying "Hey Noel, you can admit it's real now" according to several reports, apparently addressing Ashley Madison chief executive Noel Biderman.
The website, part of Canada's Avid Life Media, intends to float on the London Stock Exchange. However, a question mark hangs over the IPO, which had already failed to capture the City's imaginations, as the massive high profile hack will hardly warm investors' hearts.