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They call themselves the Impact Team and seem to have formed solely to carry out the attack on the infidelity website. There is no evidence of the group stealing data elsewhere before it announced itself with the Ashley Madison attack on 15 July.
Comments made by Noel Biderman, chief executive of Avid Life Media, which owns Ashley Madison, soon after the hack became public suggested it knew the identity of at least one of the people involved.
"It was definitely a person here that was not an employee but certainly had touched our technical services," he told security blogger Brian Krebs.
Since then, little new information has been made public about the hack, leading some to assume that the information Avid had about a suspect would soon lead to an arrest.
But it did not, and now gigabytes of information have been released and no-one is any the wiser about who the hackers are, where they are located and why they attacked the site.
The group is technically pretty competent, according to independent security researcher The Grugq, who asked to remain anonymous.
"Ashley Madison seems to have been better protected than some of the other places that have been hit recently, so maybe the crew had a stronger skill set than normal," he told the BBC.
They have also shown that they are adept when it comes to sharing what they stole, said forensic security specialist Erik Cabetas in a detailed analysis of the data.
The data was leaked first via the Tor network because it is good at obscuring the location and identity of anyone using it. However, Mr Cabetas said the group had taken extra steps to ensure their dark web identities were not matched with their real-life identities.
The Impact Team dumped the data via a server that only gave out basic web and text data - leaving little forensic information to go on. In addition, the data files seem to have been pruned of extraneous information that could give a clue about who took them and how the hack was carried out.
The only potential lead that any investigator has is in the unique encryption key used to digitally sign the dumped files. Mr Cabetas said this was being employed to confirm the files were authentic and not fakes. But he said it could also be used to identify someone if they were ever caught.
But he warned that using Tor was not foolproof. High-profile hackers, including Ross Ulbricht, of Silk Road, have been caught because they inadvertently left identifiable information on Tor sites.
The Grugq has also warned about the dangers of neglecting operational security (known as opsec) and how extreme vigilance was needed to ensure no incriminating traces were left behind.
"Most opsec mistakes that hackers make are made early in their career," he said. "If they keep at it without changing their identifiers and handles (something that is harder for cybercriminals who need to maintain their reputation), then finding their mistakes is usually a matter of finding their earliest errors."
"I suspect they have a good chance of getting away because they haven't linked to any other identifiers. They've used Tor, and they've kept themselves pretty clean," he said. "There doesn't seem to be anything in their dumps or in their missives that would expose them."
The Grugq said it would need forensic data recovered from Ashley Madison around the time of the attack to track them down. But he said that if the attackers were skilled they might not have left much behind.
"If they go dark and never do anything again (related to the identities used for AM) then they will likely never be caught," he said.
Mr Cabetas agreed and said they would probably be unearthed only if they spilled information to someone outside the group.
"Nobody keeps something like this a secret. If the attackers tell anybody, they're likely going to get caught," he wrote.
A lot of data has been released about Ashley Madison but some facts of the breach of the dating website's database remain stubbornly elusive, not least who are the hackers behind the attack?

Mohammed Haji Sadiq, of Cyncoed, entered the not guilty pleas at a hearing on Friday.
The allegations involve four girls, aged between five and 11, and allegedly took place at the Madina mosque between 1996 and 2006.
Mr Sadiq is due to stand trial later in June.
He is charged with eight counts of assaulting a girl under the age of 13 by touching and seven of indecent assault of a girl under the age of 14.
Mr Sadiq taught at the mosque between 1976 and 2006. It is understood he has had no involvement with the mosque since then.
An 80-year-old man who taught at a Cardiff mosque has denied 15 child sex offences at Cardiff Crown Court.

The 32-year-old was handed a six-month ban last August for breaching betting rules and retired two weeks later.
He was appointed player welfare manager at Super League side Warrington in October and he will retain his role with the Wolves.
"It's an exciting time and I'm really looking forward to it," Mathers told BBC Radio Leeds.
"I stick by what I said when I retired and I stand by my reasons for doing that.
"I think the old romantic in me wants to be a part of getting the Bulls back in the Super League."

Bradford Bulls have signed full-back Richie Mathers, four months after he announced his retirement from the game.

