The tech website it was given a contact email address for the hackers, who call themselves the Impact Team, by an intermediary. The hackers replied with a message signed with the same signature and fingerprint, known as a PGP key, posted with the Ashley Madison data dumps this week, Motherboard said.
"We were in Avid Life Media a long time to understand and get everything," the website quoted the hackers as saying. "Nobody was watching. No security."
Representatives of Ashley Madison's parent company Avid Life Media could not immediately be reached for comment.
Cyber security experts said data dumps on Tuesday and Thursday by the group appeared to be authentic. Tuesday's release had customer information that included U.S. Government officials, British civil servants and high-level executives at European and North America corporations.
Motherboard reported that in its exchange with the hackers, they said they had 300 gigabytes of employee emails and internal documents, "tens of thousands of Ashley Madison users pictures" and user chat messages from the site. On Tuesday, hackers released 10 gigabytes of data.