An attacker has hacked into the ABC and dumped almost 45,000 user email addresses and hashed passwords following a broadcast of an interview with radical Dutch politician Geert Wilders.
The ABC confirmed the attack, which targeted the 2010 program "Making Australia Happy" and exposed users who registered with the program's website.
Spokeswoman Sally Cray said the ABC would contact the 45,000 affected users.
"As soon as the ABC was made aware of this activity the site was shut down," Cray said.
"This breach originated at an overseas location and an activist has claimed responsibility for it.
"The ABC will be in contact with audience members who have been directly affected."
Random checks against user identities listed within the 10 page online database dump returned legitimate matches.
Passwords are vulnerable. While not in clear text, the details are unsalted and encrypted with SHA-1. Online services can easily reveal some passwords.
The hacker claiming responsibility said the attack was in response to an interview broadcast on the ABC's Lateline program with the right-wing Wilders. The attacker claimed the ABC gave Wilders "a platform to spread hate".
Updated 2:30 to reflect ABC confirmation.