Hackers who claim to have infiltrated Ashley Madison - a website aimed at facilitating affairs - are threatening a major dump of sensitive user information, if the site is not permanently deleted.

Its tagline reads, "Life is short. Have an affair." The homepage claims that it is, "the world's leading married dating service for discreet encounters."

Users' information could become considerably less discreet if the group of hackers called 'The Impact Team,' who claim to have accessed the site's data follow through on threats to publish users' details from names and credit card numbers to "secret sexual fantasies."

The site has 37 million users, who are primarily based in the US and Canada.

The hackers have posted some data from Avid Life Media (ALM) - the site's parent company - ALM has confirmed that these documents are genuine - and that they were illegally obtained. 

The hackers have issued a manifesto which reads:

"Avid Life Media has been instructed to take Ashley Madison and Established Men offline permanently in all forms, or we will release all customer records, including profiles with all the customers’ secret sexual fantasies and matching credit card transactions, real names and addresses, and employee documents and emails."

The hackers have focused on the fact that Ashley Madison charges $15 to users who want to leave the site - and to delete their data. The team behind the attack claim that this function doesn't exist because the data from the card transactions closing accounts is stored.

ALM believes that the hack has come from someone who has worked with the company, it says that it is close to confirming their identification.

Data security journalist Brian Krebs broke the story. He spoke to ALM chief executive, Noel Biderman, who said, "I’ve got their profile right in front of me, all their work credentials. It was definitely a person here that was not an employee but certainly had touched our technical services."

A statement from ALM reads: “We apologise for this unprovoked and criminal intrusion into our customers’ information. The current business world has proven to be one in which no company’s online assets are safe from cyber-vandalism, with Avid Life Media being only the latest among many companies to have been attacked, despite investing in the latest privacy and security technologies."