An adult dating website got hacked and millions of people's sensitive details have been leaked

Casual dating website Adult FriendFinder has been hacked, an investigation from Channel 4 News has found - and the personal details of millions of users have been leaked.

With 63 million global users, Adult FriendFinder is one of the largest dating and casual encounter networks online. (For reference, there were an estimated 50 million Tinder users in late 2014.) But 3.9 million users' accounts have allegedly been leaked online, and are circulating in spreadsheets on forums.

The details leaked include:

• Sexual preferences
• Email addresses
• Sexual orientation
• Dates of birth
• Addresses
• Usernames
• Whether users are "seeking extramarital affairs"

Together, these pieces of information put together a comprehensive (and potentially highly compromising) picture of the victims' lives. It's not yet clear how the data was leaked - we've reached out to Adult FriendFinder and will update this story when they respond - but it opens the door to spam and blackmailing.

The leak is also highly embarrassing for Adult FriendFinder in another way. Channel 4 News analysed the data and found that almost no women actually use the adult social network. "Among the 26,939 users with a UK email address," technology producer Geoff White writes, "there are just 1,596 who identified as female: a ratio of one woman to every 16 men."

Here's the front page of Adult FriendFinder. It describes itself as a "thriving sex community" that can "satiate your need for amazing sexual experiences."

In a statement, parent company FriendFinder Networks Inc said that it "understands and fully appreciates the seriousness of the issue. We have already begun working closely with law enforcement and have launched a comprehensive investigation with the help of leading third-party forensics expert."

It adds: "We pledge to take the appropriate steps needed to protect our customers if they are affected."