Perth's new Yagan Square, which cost the government of Western Australia $56.4 million and took two years to build, was finally opened last month.
On Thursday, hackers took over the square's two electronic signboards, one at each entrance of the William Street Mall, to broadcast the homepage of a porn website Pornhub on them following a "software malfunction" that reportedly allowed an internet browser to be accessed via the touchscreens.
"Unfortunately, it appears that these screens were compromised this evening and, for a brief period of time, some inappropriate content was displayed on one of the screens", a spokeswoman for the city's Metropolitan Redevelopment Authority told the ABC.
The screens were promptly turned off, but images of the prank were already being spread via Twitter by pedestrians who happened to walk past the mall that night.
An investigation has been launched into who uploaded the Pornhub home page, the MRA spokeswoman said.
"The MRA takes this matter very seriously and will undertake a full investigation to understand how this event has happened and identify those responsible," she told reporters.