The Impact Team stated its reason for the hack, which seemed to relate to a data retention practice. The hackers said ALM had lied to users when it said it would remove personal details from its sites for a $19 fee.
The hackers claimed that Ashley Madison's full "paid-delete" feature promises "removal of site usage history and personally identifiable information from the site," but users' purchase details—including real name and address—aren't erased.
"Full Delete netted ALM $1.7mm in revenue in 2014. It's also a complete lie," the hacking group claimed in a manifesto, according to Krebs on Security, the site that broke the story.
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"Users almost always pay with credit card; their purchase details are not removed as promised, and include real name and address, which is of course the most important information the users want removed."
In a Monday statement, ALM denied these allegations. "Contrary to current media reports, and based on accusations posted online by a cyber criminal, the 'paid-delete' option offered by AshleyMadison.com does in fact remove all information related to a member's profile and communications activity," the statement said.
The company added that, in light of the hacking, it would now offer its full-delete option for free.