It was noticed by security researcher Vinny Troia who pointed out that the group was back with new data for sale.
Nitro, a company that was started in Melbourne, has been insistent that the breach is "an isolated security incident" as stated when it posted a notice to the ASX on 21 October.
However, the cyber security firm Cyble has released details about the incident, which indicate that it was much bigger than has been made out.
"The database contains emails and hashed passwords," he added.
Actor selling the database of Nitro containing 77,000,000 users.— Alon Gal (Under the Breach) (@UnderTheBreach) October 29, 2020
Nitro is a software used to create, edit, sign, and secure Portable Document Format files so there is risk the hacker also stole sensitive documents.
The database contains emails and hashed passwords. pic.twitter.com/FnWF7Kxyps
iTWire informed Nitro Software about the database being advertised for sale and asked for the company's response. A spokesperson offered the same comment as it had earlier on Thursday, when iTWire asked for its take on various claims made by Cyble.
"Nitro is not in a position to provide further comment while the investigation is ongoing," a spokesperson said.
"We are continuing to communicate with our customers and will provide updates via the Nitro security page as more details become available."
Nitro has its headquarters in San Francisco and also has offices in Dublin and Melbourne.