The personal details of almost 50,000 internet users have been exposed online after the ABC's main website was hacked.
A subdomain of abc.net.au was infiltrated early on Wednesday morning and the passwords, usernames, email addresses, location and postcodes of people who'd made comments on the site were posted on the internet.
"Overnight the ABC was made aware that an ABC television program website was hacked," the corporation told AAP via an emailed statement.
"The website relates to the ABC television program Making Australia Ha ppy, which aired in late 2010.
"At this stage, we are still investigating the details of the breach.
"However, we do know that it has exposed the name, username and a hashed version of the password that audience members used to register on the program website.
"As soon as the ABC was made aware of this activity the site was shut down."
The ABC said the attack originated overseas.
ABC Radio Melbourne tweeted: "Claims ABC website has been hacked - reports up to 50,000 emails have been accessed."
The hacker claiming responsibility said it was in response to the ABC interviewing controversial Dutch anti-Islam politician Geert Wilders.
A Twitter user called Phr0zenMyst said: "ABC hacked for giving a platform to Geert Wilders to spread hatred #OpWilders - database leaked!"
Mr Wilders was interviewed by Lateline during his recent visit to Australia.
NSW resident Tim Gresham told News Ltd he was horrified to learn his personal details had been exposed.
The details were published along with 49,561 other ABC website users' data, on a website linked to Anonymous.
"This hacker has probably got a lot of information about me, intimate information about me, having an idea of what that website asked me in terms of my relationships and personal life," Mr Gresham said.
"They're asking a lot of people some very intimate stuff on that website, so these hackers have got some fairly intimate information on a number of people if they've managed to hack that website. This is big."
Sign up for CIO Asia eNewsletters.