An adultery website with 37 million members looking for secret affairs has been hacked and some personal details posted online.
Hackers have stolen and leaked personal information from Ashley Madison, an international dating site with the tagline: "Life is short. Have an affair."
A group calling themselves The Impact Team claims it has complete access to Ashley Madison's database of members.
It says it also has financial records and other personal information that it is threatening to publish online unless the site closes.
For now the group has released just 40MB of data, including some credit card details and several documents about its parent company Avid Life Media (ALM), it is reported.
But the group says it is prepared to release all customer records, including the "secret sexual fantasies" of members, unless the site is closed.
The group has also compromised two other dating sites; Cougar Life and Established Men.
These sites are also owned by ALM.
The hackers said in a statement: "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 other websites may stay online."
The hackers' main issue with the adultery site seems to be a leavers' fee that the company charges users.
The site offers a "full delete" of data for a fee should a user choose to leave the service permanently.
Although it is possible to be anonymous on the site for free, Ashley Madison says the delete option is a way to remove data from their servers.
But The Impact Team claims that details such as real name and address are never deleted.
In their own statement, ALM said: "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.
"At this time, we have been able to secure our sites, and close the unauthorised access points. We are working with law enforcement agencies, which are investigating this criminal act.
"Any and all parties responsible for this act of cyber-terrorism will be held responsible."
In a 2012 study by online rights campaign group EFF, Ashley Madison was praised for the way it deleted data after a user closed their account.