The site boasts 63 million users worldwide and claims more than 7 million British members.
The spreadsheets contain addresses linked to dozens of government and armed services personnel, including members of the British Army.
"Where you've got names, dates of birth, ZIP codes, then that provides an opportunity to actually target specific individuals whether they be in government or healthcare for example, so you can profile that person and send more targeted blackmail-type emails," says Charlie Mc Murdie, a cybercrime specialist for Pw C and former head of the Metropolitan Police's electronic crime unit.
The front page of Adult Friend Finder, which is based in California, features photos of dozens of attractive young women.
The stolen data reveals the sexual preferences of users, whether they're gay or straight, and even indicates which ones might be seeking extramarital affairs.
In addition, the hackers have revealed email addresses, usernames, dates of birth, postal codes and unique internet addresses of users' computers.
Channel 4 News has been investigating the cyber underworld, discovering which websites have been hacked and exposing the trade in personal information of millions of people through so-called "dark web" sites.
The investigation led to a secretive forum in which a hacker nicknamed ROR[RG] posted the details of users of Adult Friend Finder.
"The site seemed OK, but when I got into it I realised it wasn't really for me, I was looking for something longer term. You couldn't get into the site without handing over information.
"I deleted my account, so I thought the information had gone.