At first glance, the profiles seem innocent enough. There's Lucy, 31, from Rochester, who enjoys cooking, theatre and books, and Jack, 46, from Hampshire, who describes himself as a "laid-back character who travels a lot with work and loves music and sport".

Some of the requests even sound rather sweet. Matthew, a 59-year-old Londoner, hopes to meet a woman to "chat about life in general, politics, faith and social justice", while Sally, 43, from Hertfordshire, wants "someone to keep me on my toes and make my pulse race".

They could all be hopefuls on an ordinary dating website - one of the many that have sprung up in recent years to help single men and women find love through the internet.
But these profiles are far more sinister than that. For the people behind them are all, in fact, married. They are signed up to Ashley Madison, a controversial website that promotes and caters for extra-marital affairs.

One can only imagine the huge wave of terror felt by them yesterday when a group of hackers threatened to reveal the identities of Ashley Madison's members.

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One of the site's many opponents, a secretive group calling themselves The Impact Team, claim to have hacked into the online database and stolen the details and private messages. They warn that unless the site is shut down with immediate effect, they will expose its 37 million cheating users worldwide by publishing their names, addresses and explicit images online.

Desperate to limit the damage, Canadian-based Ashley Madison appears to have caved in to some of their demands by suspending a $30 fee for members wanting to wipe their accounts - a bone of contention for the hackers, who said that the payers' details would still be kept on the company's system.

It remains to be seen, however, if this will placate the hackers.

Ashley Madison - whose slogan urges "Life is short, have an affair" - says that exposing the identity of its members would breach their right to privacy.

Others argue that the spouses of cheating partners have a right to know what their other half is doing.

For in the years since Ashley Madison launched in the UK in 2010, the site has been responsible for many ruined marriages and relationships.

And while members make no mention of children on their profile, their online actions are destroying families offline.

One of those hurt wives is Sarah Gould, 34, from Kingston upon Thames, Surrey, who until January 2013 was happily married - or so she thought - to Rich, 36, a computer engineer. They'd been wed for ten years, had a six-year-old son, James, and lived in a three-bedroom house in a pretty cul-de-sac.

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"We had a gorgeous family and were very loving and close-knit," says Sarah. "We had a wide social circle and got on well with each other's parents. I'd worked as an accountant, but gave it up when we had James. I was happy staying at home and just being a mum."

Then, one day in January 2013, Sarah was at home when the kitchen sink sprung a leak.

"I switched on Rich's laptop to try to search for a plumber nearby, and suddenly I heard this pinging noise and a little window popped up on the corner of his screen," she says.

"I clicked on it and it took me through to this website, which at first glance looked like a dating website, but then I saw it was all about cheating on your wife.

Is monogamy dead? Ashley Madison creator thinks so. Photo / Thinkstock
Is monogamy dead? Ashley Madison creator thinks so. Photo / Thinkstock

"There was a series of messages between Rich and half a dozen women. He was deep in conversation with one called Alison, whose screen name was 'Sexy77."

Shocked, Sarah slammed the laptop shut and called a friend to come round and take a second look.

"I was shaking from head to foot," she says. "I felt physically sick. I didn't know whether to cry, laugh or scream. It was horrendous.

"My stomach was in knots. I felt so angry and confused and utterly heart-broken, all at the same time."

With her friend's support, she phoned Rich at work, asked him to come home and confronted him about what she had found.

"He admitted it right away," she says.

"He'd been seeing this woman for two years. He found her on this website and they'd been meeting up ever since. I threw him out the next day and never looked back. Eight months later, our divorce came through."

As his job involved computers, Sarah had never been suspicious about her husband's internet use.

"He'd sit with the laptop on his knee from 7pm to 9pm most nights," she says. "I'm not technologically literate so there were no red flags.

"I didn't even know sites like Ashley Madison existed. They're so vile and dishonest, making it all sound like a bit of fun. I can't bear to think about what sort of woman would go on there to find a married man.

"She was local, the same age as me, and married herself - which made it even worse."

Harder still, she admits, has been dealing with the impact of her divorce on her son.

"I got custody and Rich pays maintenance, but it's been hard for my son. I still haven't found a way to explain what his daddy did that was so bad."

Sarah found support through Women Scorned, a non-profit group for women who have been cheated on by their husbands or partners.

Jo Welch, the group's commercial director, says the number of messages they have had from those whose marriages have broken down due to infidelity websites such as Ashley Madison has soared in recent years.

"It may have started in the US but it's a trend that is growing frighteningly quickly in Britain," she says.

"Websites like this are disgraceful. They break up families, causing so much pain and suffering - and we have to deal with the children and wives and husbands whose lives are destroyed at the click of a button."

Despite the extreme ramifications of joining the site, Ashley Madison is astonishingly easy to use. Free to join, new members are asked to provide a user name and blurred photograph (the site will pixelate it for you or you can add a "disguise", such as a mask).

Users then select what they're looking for, ranging from "cyber affair/erotic chat" to "anything goes". It's open to single and attached users, though those who sign up are predominantly married.

Men then pay in "credits".

The introductory package is about $60 for 100 credits or about $350 for an "affair guarantee" membership of 1,000 credits. Five credits buys a message to another member and 30 gets you 30 minutes of live chat.

Women don't have to pay - a sensible incentive, given that 70 per cent of the site's profiles are male.

They can then send private messages, "winks" to notify another user that you have viewed their profile or virtual gifts (normally images), and chat via instant messenger when both members are online.

But what really sets Ashley Madison apart from other infidelity websites is its brazen approach to cheating.

Founder Noel Biderman - a married father of two from Canada who set up the company with his wife Amanda - has claimed that affairs could be good for a marriage as they remove the stress of sexual frustration.

Biderman, who was a sports lawyer before he turned internet entrepeneur, is said to have made anything up to $1 billion from the site and has declared "monogamy is dead".

The site's logo makes a cruel mockery of marriage, with the 'o' in the shape of a wedding ring. Some users speak in code - "ziplining" is code for having an affair - while others boast about being "honeymooners": married less than three years.

Despite the hackers' threat hanging over the site, yesterday there was no sign of it deterring Britain's married men from straying. Within an hour of signing up as a new female member, without a profile picture or any identifying details except a user name, age and location, I was contacted by 16 men, 13 of them married.

One wanted to chat privately; another asked to share his intimate photo album. A few hadn't bothered to obscure their faces in their profile pictures. One even looked as if he was at his own wedding.

Worse than breaking up individual marriages, experts say Ashley Madison and its ilk are doing untold damage to the institution as a whole. Harry Benson, research director at the Marriage Foundation, says such sites are "thoroughly unpleasant and misleading".

"They actively encourage people to look for an affair by making that option available," he adds.

"Every marriage goes through difficult times, when you feel like you're not being listened to or cared for, and affairs do happen.

"But to facilitate it is trying to profit from unhappiness and turn it into misery. To pretend that adultery is a good thing in an otherwise long-lasting, loyal relationship is utter nonsense."

So do its users deserve to have their identities exposed?

Divorce lawyer Georgina Hamblin, director of leading family law firm Vardags, says not: "Whatever you think of the morals of the people who sign up to use sites like Ashley Madison, they do have a right to privacy. Hacking into a database and threatening to reveal their personal details shouldn't be condoned."

But, fascinatingly, Georgina has found that profiles on infidelity websites are now increasingly cited in divorce petitions as grounds for the 'unreasonable behaviour' of one partner.

"We're seeing a huge trend in this type of work," she explains. "It's an adulterous minefield. Every third client now has something to do with online infidelity."

She is working on a case in which a husband signed up to an extra-marital affairs site in order to catch out his unfaithful wife. "It's been incredibly hurtful - images found on the family iPad, children involved, decades of marriage. But situations like this are becoming all too common."

For Sarah Gould, who mentioned her husband's extra-marital dating profile in her divorce petition, it sounds painfully familiar.

"I am very happily divorced, but if it hadn't been for that website, then I might still have been happily married," she says, sadly.

"What those hackers are doing is brilliant. Let the cheaters sweat. They only have themselves to blame if the whole world finds out their dirty little secret."

• Names have been changed for legal reasons.