WASHINGTON (AFP) - Hackers breached the online adultery website Ashley Madison and threatened to expose data on users in an effort to shut down the service which claims millions of members worldwide.

Avid Life Media, which owns Ashley Madison, said in a statement Monday an "unauthorized party" was able to gain access to the data through various unauthorized points on the website.

A group calling itself "the Impact Team" claimed responsibility and said it was part of an effort to shut down Ashley Madison, known for its slogan, "Life is short. Have an affair." The group, in statements posted online, said that Ashley Madison and a related site called Established Men "must shut down immediately permanently." "Shutting down AM and EM will cost you, but non-compliance will cost you more," the statement said.

"We will release all customer records, profiles with all the customers' sexual fantasies, nude pictures, and conversations and matching credit card transactions, real names and addresses."

Posts removed

Avid Life, which is based in Canada, said some personally identifiable information was posted online before being removed.

"Our team has now successfully removed the posts related to this incident ... about our users published online," Avid Life Media said.

"At this time, we have been able to secure our sites, and close the unauthorized access points," the company said.

"We apologize for this unprovoked and criminal intrusion into our customers' information." Ashley Madison, which boasts more than 33 million users, helps people who are in relationships cheat on their partners. With its other dating services, Avid Life says it is Canada's largest dot-com with some 40 million members.

It said it has "stringent security measures in place, including working with leading IT vendors from around the world." "These security measures have unfortunately not prevented this attack to our system," Avid Life added.

The company said it is working with law enforcement over the breach and that those responsible for the "act of cyber-terrorism will be held responsible." Users in more than 46 countries subscribe to the cheating website, which was founded in 2001.

The Canada-based company said a new user joins every six seconds, and that it is "the world's largest website for married men and women looking to have a discreet affair." The incident is the latest in a series of high-profile data breaches affecting companies as well as government databases.

It comes two months after a leak of stolen data from 3.9 million members of Adult FriendFinder, which claims to be ""the world's largest sex and swinger" community.

Toronto-based Avid Life said recently it was considering a stock flotation to help grow the business, which also includes the website for women called Cougar Life, aimed at the "recently divorced, single mom or sexy single still on the prowl."

Avid Life chief executive Noel Biderman told security blogger Brian Krebs the company was close to identifying the source of the breach.

"It was definitely a person here that was not an employee but certainly had touched our technical services," he was quoted as saying.