"The Eden Park Trust and venue systems are separate from O'Brien Group systems and at no time was any data at risk of breach," the spokeswoman said.
"Trust data is well protected in line with cybersecurity best-practice, and our security measures are continuously monitored to ensure all networks and databases remain secure."
O'Brien Group did not immediately respond to a request for comment.
A ransomware specialist with a New Zealand-based company told the Herald he had cited a post by the LockBit ransomware gang on the dark web. LockBit provided a link to download what it said were O'Brien Group files.
The O'Brien Group operates a string of venues in Australia, including The Gabba and Suncorp Stadium in Brisbane, the Adelaide Showground, and a number of boutique hotels.
There have been no reports of its operations being disrupted.
The cybersecurity specialist said the appearance of files online could be an indication that the victim has refused to pay up - although drip-feeding stolen files into the public arena could also be sued as a pressure tactic.
GCSB director-general Andrew Hampton recently warned about a possible rise in attacks by ransomware gangs - many of whom are based in Russia or Eastern Europe.
Hampton said that while ransomware attackers were usually commercially motivated, a number had threatened revenge attacks on targets in countries that have supported Ukraine.