A cache of date stolen from the site, which is owned by Canadian company Avid Life Media, includes databases and financial information. Avid said it was investigating the security breach to identify the nature and scope of it and also working with authorities on a criminal probe.
The company, which also runs other dating sites cougarlife.com and establishedmen.com and has a combined 40m customers, apologised to users who have been threatened with having their details leaked, including names, credit card details as well as more personal information about their activities on the website.
"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," the company said in a statement.
The hack was identified by the website KrebsOnSecurity, which monitors cyber security, identifying The Impact Team as the group behind it.