Nearly one million Australians risk being exposed as unfaithful partners in the hacking saga of infidelity dating site Ashley Madison.

The site, which targets users looking for sex outside of their marriages, is being blackmailed by a group calling itself The Impact Team, which has threatened to publicly release customers' profiles and credit card details.

Ashley Madison: up to 1 million Australians could be exposed.

In a statement released on Monday, The Impact Team warned ALM to remove the Ashley Madison and Established Men sites 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".