The United Australia Party and Trumpet of Patriots, both funded by Mr Palmer, noticed unauthorised access to their servers, resulting in the "exfiltration" of data records on June 23.
"We were the subject of a ransomware cyber-attack," the parties said in a statement.
Personal information such as email addresses, phone numbers, identity records, banking details, employment history, documents provided under confidentiality arrangements and "the like" have been exposed.
"We do not know comprehensively what information of yours was on the server but you should assume that any information you have provided would have been stored on the server," the parties said.
"We do not keep a record of all individuals who were on the server.
"We have determined it is impracticable to notify individuals."
It's been recommended that anyone review emails they have sent to the United Australia Party or Trumpet of Patriots to identify the information that could have been exposed.
Supporters should "carefully consider" whether they need to take any action on the assumption their data has been compromised, the parties said.
This may include monitoring bank accounts and contacting their financial institution, changing passwords and being "vigilant about use of your identity".
The parties also warned to keep an eye out for phishing scam attempts in the wake of the cyber attack.
"We sincerely apologise for this incident and are taking steps to ensure it does not happen again," they said.
A cybersecurity company has slammed the parties' decision not to contact individuals about what data was compromised.
It also criticised Mr Palmer's parties for failing to notify supports for a month.
"For nearly one month, threat actors have potentially had access to tens of thousands of people's bank records, identity records, documents subject to confidentiality arrangements, employment history, email addresses and phone numbers," Tony Jarvis from Darktrace said.
"I would urge anyone who has ever contacted either party to immediately implement steps to secure their accounts."
The United Australia Party was formed by mining magnate Mr Palmer in 2013 but has struggled to win federal seats despite running candidates in hundreds of electorates.
In the 2022 election, the party failed to win any House of Representatives seats and just one Senate position, leading to it deregistering.
The party was unable to register for the 2025 election, sparking Mr Palmer to launch the Trumpet of Patriots in February, looking to lift many of the policies put forward by US President Donald Trump.
Trumpet of Patriots failed to secure any seats in the House of Representatives in the 2025 election.
Mr Palmer was an MP for the United Australia Party for one term in 2013 and is now the chairman of both parties, using his fortune to spend millions of dollars on election advertising.
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