The whistleblower who exposed the illegitimate access of millions of people's Facebook data says it is overwhelmingly likely a foreign country targeted this year's Australian election.

Christopher Wylie, who blew the whistle on collapsed consulting firm Cambridge Analytica, also names China as a greater and "far more sophisticated" threat to Australia than Russia.

Cambridge Analytica whisteblower Christopher Wylie says China poses a particular digital threat to Australia. Credit:Dominic Lorrimer

"Australia is not immune to it," he says of the global hacking threat. "If people think that because you're a smaller country you're not a target, then that's a dangerous belief to have."

Unlike in the United States or the United Kingdom, where Cambridge Analytica worked to influence the 2016 election and Brexit vote respectively, Mr Wylie says China is the greater online threat to Australia than Russia.