The presidential election campaign of Donald Trump says its official website was defaced earlier on Tuesday and that it is working with law enforcement to investigate the source of the attack.
The campaign said in an emailed statement there was "no exposure to sensitive data because none of it is actually stored on the site."
The FBI declined to comment.
The Trump website seemed to be fully functional Tuesday. Screenshots circulating online appeared to show that the site had briefly displayed a bogus message spoofing a law enforcement announcement.
The message then sought cryptocurrency donations from visitors in exchange for access to purported "internal and secret conversations" from Trump's family and associates.
The hackers provided no evidence to back their statements.
Past boasts by hackers to have inside access to Trump-related correspondence - notably by a group that claimed to have penetrated an entertainment law firm earlier this year - have come to nothing.