The man cashing in on infidelity ... Noel Biderman.

The man cashing in on infidelity ... Noel Biderman.

The online dating service that outraged America has opened for business down under and Australian women are apparently relishing the temptation.

Weeks into a "soft opening" here, with no publicity or advertising, Australian women have adopted the Ashley Madison agency motto - "life is short, have an affair" - with an enthusiasm founder Noel Biderman says he's not seen before.

I wouldn't have 5.5 million members if I wasn't doing something right ... The threats against me exist, it's a sad fact of life 

"We've never had more women than men, it's always been about two to one, male to female (membership)," Biderman said.

"Australia has this unique factor, which could be an early adopter situation, it's about 36 per cent female, and that's about six per cent more than in any other city we've ever encountered on the female side."

In Sydney to officially launch an Australian version of his online dating service for married or attached men and women, Biderman - known in the US as the "King Pin of Infidelity" - defended his controversial venture.

"Marriage is looked at as this institution that never changes but that's just nonsense," the married father of two said.

"It's really only fairly recently that you chose your partner or married for love and one of the consequences of that is this rapid and high divorce rate we've seen throughout the world.

"Ultimately, the institution is always going to keep evolving and when something is not in our DNA, and monogamy is surely not in our DNA, then you can't help but wonder if it's on its last legs.

"I wouldn't have 5.5 million members if I wasn't doing something right."

But the former sports lawyer's success has not been without pitfalls.

Biderman arrived in Sydney with a security detail, a necessary evil born of what he says is other people's misguided reaction to what the Ashley Madison agency does.

"The threats against me exist, it's a sad fact of life," he said.

"Rather than take a look at themselves in the mirror and wonder what's gone wrong in their relationship that would lead a partner to stray, people have fired off emails accusing me of being responsible for the breakdown of their relationship.

"It's been everything from having a spouse getting verbally aggressive with me ... to people sending emails saying I've ruined their lives, or created a situation that has irreparably damaged a relationship and that I'll burn in hell."

And while the Australian reaction to date has not mirrored the outraged condemnation from pundits in the US, Biderman's unique service has still drawn some criticism.

"I think the notion that having an affair on the side is a harmless activity that has no consequence or implication for your marriage, partner or your family ... is a very misguided view," Relationships Australia chief executive Anne Hollands said.

"And it's often a justification used by people who are seeking to escape their circumstances for one reason or another."

Biderman said 40,000 Australians so far had joined the agency, which he started in Canada in 2001, fusing the two most popular children's names at the time to come up with AshleyMadison.com.

Membership is expected to grow to more than one million once a provocative television, billboard and online advertising campaign kicks off, he said.

The agency is free to join and works much like other dating services.

Users buy packages of "credits" for between $49 and $249 that enable them to interact with other users by way of a virtual wink, smile or rose.

Biderman said men and women joined for different reasons.

"I think ultimately for men it's about sex, this is about an absence of sex in their lives or sex being too 'vanilla' and they're looking for different flavours," he said.

"I think with women it's a bit more complicated, to be honest with you.

Some women were looking for the "lifestyle benefits" that might accompany the mistress status, while others wanted to continue being objects of desire, Biderman said.

"They're not being brought flowers anymore and they're not being paid attention to so they're looking to rekindle that feeling," he said.

Anne Hollands said infidelity was an extreme and risky reaction to such a problem.

"An affair is not going to make that situation any better and usually it becomes rather addictive, the high that you get from these sorts of liaisons is something that you keep wanting to seek again and again," she said.

But Biderman maintains the odd taste of illicit romance need not be the deal breaker it's made out to be.

"People who are happy in a monogamous marriage, that's incredible," he said.

"I'm just suggesting that the world over it seems to be that tens and tens of millions of people are not happy, at least when it comes to their sex lives.

"They're not necessarily willing to leave their partners, they're just looking for something on the side and maybe there's nothing wrong with that."

Are Australian women more prone to cheating? Have your say in the Essential Baby forums.