Corporation spokesman Sally Cray said she was aware of reports that a subdomain of abc.net.au had been infiltrated and IT experts were examining the source.
"We're looking into it and we're trying to figure out whether it has actually happened, and if it has happened," she told ABC radio.
There were reports that people who had posted comments on the site had had their usernames and passwords leaked online.
A hacker linked to the online vigilante group Anonymous has claimed responsibility for the attack, saying it was in response to the corporation giving airtime to the Dutch MP Wilders.
Mr Wilders was interviewed by the ABC's Lateline program during his recent visit to Australia.
Ms Cray said the corporation would issue an update on the situation later on Wednesday.