Looks like they put in the least possible effort. "Why?" Hogan/ATO need the money:
Hogan and his then collaborator John Cornell were the most high-profile targets of Project Wickenby, a joint ATO and Australian Crime Commission investigation into money aundering and tax evasion using overseas accounts.
The ATO initially pursued the duo for unpaid tax in excess of $150 million, claiming they had evaded tax by channelling the massive profits from the Crocodile Dundee franchise through a series of overseas tax havens.
In 2012, after five years of legal wrangling and the dropping of the criminal investigation, Hogan and Cornell reached a confidential settlement with the ATO.