Who was responsible for leaking the Ashley Madison data?

The Ashley Madison data leak, which occurred in July 2015, was orchestrated by a group or individual known as The Impact Team. They infiltrated the systems of the Ashley Madison website, whose parent company is Avid Life Media (ALM), and obtained sensitive information pertaining to its users. The Impact Team justified their actions by alleging that Ashley Madison had lied about a service that claimed to erase user data for a fee but failed to do so. In protest against the website's morally questionable premise, which facilitates extramarital affairs, and out of apparent frustration with the deceptive practices of ALM, The Impact Team released the personal details of millions of users, effecting widespread personal and professional repercussions for those individuals whose information was exposed.