With Russia at war with Ukraine, keeping our secrets safe from Moscow is vital. 
But history tells us Australia hasn't been very good at spying on spies and knowing when our agencies have been infiltrated. 
Today, investigative reporters Sally Neighbour and Margot O'Neill on an ASIO mole who sold our intelligence to the Russians, and why our spy agency kept it secret for so long. 
Featured: 
Sally Neighbour, investigative reporter, ABC Four Corners and ABC iview 
Margot O’Neill, investigative reporter, ABC Four Corners and ABC iview