AshleyMadison.com's owner said it is examining a large batch of data posted online by hackers who breached the website last month.
A group calling itself Impact Team initially posted a sample of the data online on July 19, giving the site's owner, Avid Life Media, a month to shut down AshleyMadison.com and another site, Establishedmen.com.
The group in part contested the moral position of Ashley Madison, which caters to people seeking extramarital affairs.
Avid Life Media, based in Toronto, said in a statement that it is "actively monitoring and investigating this situation to determine the validity of any information posted online."
"This event is not an act of hacktivism, it is an act of criminality," the company said.
Avid Life Media has hired independent forensic investigators and is working with the Royal Canadian Mounted Police, the Ontario Provincial Police, the Toronto Police Services and the FBI.
In a note on Pastebin, Impact Team claimed it had exposed the fraud, deceit and stupidity of Avid Life Media, including links to the files posted on the sharing service Mega and a torrent file.
The file posted on Mega appears to be 8.68 GB and is titled ashleymadison_db_dump. The links to the files on Mega, however, were quickly disabled late Tuesday.
When a 40 MB sample of the data was released in July, Avid Life Media said it used Digital Millennium Copyright Act (DMCA) requests to get the material removed from online services, and it appears to be taking the same tact this time around.
The sample data consisted of customer records, including email addresses, and sales and marketing data.
At the time, Impact Team claimed it found the paid-for feature to delete account registrations with Ashley Madison didn't in fact work.
The website had charged $19 to scrub data. Avid Life Media contested that assertion the feature didn't fully delete information but subsequently stopped charging for it.