Hackers target 412 million accounts on the world's number one adult dating site.

Millions of people have been exposed by an unprecedented attack on AdultFriendFinder.com, a sex and swinger website that self-describes as the world’s “number one adult dating site”.

Nearly 340 million account holders may have had personal information including email addresses, passwords, dates of last visits, browser information, IP addresses and site membership status accessed, according to News.com.au.

The breach occurred last month, but data experts are only now coming to terms with the scale of it – some have labelled it the largest attack of its kind.

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It’s also the second time the website has been targeted in just over a year raising serious questions over the site’s security practices.

A number of other sites in the Adult Friend Finder network have also been affected, including porn sites Penthouse, Stripshow and iCams, with The Guardian reporting total number of users affected by the incident could be as many 412 million.

For scale, the 2013 MySpace leak affected 359 million users, while in last year’s hack of adultery site Ashley Madison 33 million user accounts were compromised.

Only the 2014 Yahoo attack of 2014 was bigger, affecting as many as 500 million users.

While most of the information taken won’t be of use to criminal gangs, nearly 16 million deleted accounts from the Adult Friend Finder Network were also accessed, News.com.au reported, raising serious questions about why the company kept details of former users for so long.

Soon after the attack occurred the network’s vice president Diana Ballou released a statement saying: “We are aware of reports of a security incident, and we are currently investigating to determine the validity of the reports.”

The perpetrator of the attack has yet to be revealed.