One of the world's biggest adult dating sites, Adult FriendFinder.com (AFF) has been hacked, exposing sensitive information – email addresses, sexual preferences and even whether a spouse has cheated – of milions of its members.

A recent investigative report regarding the cyber underworld, a secret forum, revealed the information of 3.9 million members of Adult FriendFinder, including those who had long quit the site, according to Channel 4 News.

Adult FriendFinder, owned by FriendFinder Networks Inc told Channel 4 News that they are working with law enforcement agencies especially third-party forensics and would come to the aid of members affected by the incident.

AFF, which boasts 64 million members has been marketing itself as the best site for dates, hook-ups, swinging partners and sex communities does not maintain any of the pretense about finding life-long love that other dating sites use, the Wall Street Journal said in a related report.

The exposed data of AFF's members could be used to send virus mail or even identify potential blackmail targets, the publication said.