Evan Leslie McMahon, 21, was arrested after the Australian Federal Police were alerted by the FBI to his alleged activities via a website called WickedGen.com in May 2018.

It is alleged the account generator operated for about two years, selling details stolen from unknown victims in Australia and abroad - including the United States - for online subscription services such as Netflix, Spotify and Hulu.

The AFP alleges the account details were obtained through "credential stuffing", in which a list of previously-stolen or leaked usernames, email addresses and corresponding passwords are re-used and sold for unauthorised access.

Before the website was shut down, it claimed it had more than 120,000 users and almost one million sets of account details.

"Police will allege the administrator of WickedGen made an estimated AUD$300,000 selling the stolen account subscriptions through this website, and other similar sites identified through the course of investigations," the AFP said in a statement on Wednesday.

McMahon was charged with multiple cybercrime offences and appeared via video link at Sydney's Central Local Court on Wednesday.

He was granted strict conditional bail with a $200,000 surety and was ordered not to access the internet apart from his workplace and have only one phone with no internet capacity.

McMahon's LinkedIn profile lists him as web developer at personal finance comparison website Finder.

The company on Wednesday confirmed he was a "former employee".

"The investigation centres around activities that commenced prior to Evan's employment and are unrelated to Finder. It involves the inappropriate use of online subscription credentials from other websites," it said in a statement to AAP.

"We can't comment further at this stage as the matter is before the courts."

The man's lawyer Mark Peoples told reporters outside court it was a "very complicated computer fraud-type case".

The matter is due to return to the Downing Centre Local Court on May 7.

Australian Associated Press