Almost 10 million Aussies have had their personal details compromised following a major cyber attack on Optus last week.
The attack is currently being investigated by the Australian Federal Police, who are working to identify the people behind the breach and to prevent identity fraud of those affected.
"We are aware of reports of stolen data being sold on the dark web and that is why the AFP is monitoring the dark web using a range of specialist capabilities," said Assistant Commissioner of Cyber Command Justine Gough.
"Criminals, who use pseudonyms and anonymising technology, can't see us but I can tell you that we can see them."
Optus announced they were hit by the attack last Thursday, saying they immediately shut the breach down.
"We are devastated to discover that we have been subject to a cyberattack that has resulted in the disclosure of our customers’ personal information to someone who shouldn’t see it," Optus CEO, Kelly Bayer Rosmarin, said at the time.
"We are very sorry and understand customers will be concerned. Please be assured that we are working hard, and engaging with all the relevant authorities and organisations, to help safeguard our customers as much as possible."
Slater and Gordon Lawyers are investigating whether to launch a class action lawsuit against Optus on behalf of former and current customers.
Class actions senior associate Ben Zocco said the leaked information posed a risk to vulnerable people, including domestic violence survivors and victims of stalking.