I'm an FBI spy hunter. This is the biggest threat we face... and it could destroy us all

Robert Hanssen was the most damaging spy in American history. A senior FBI agent turned traitor, he sold classified secrets to Russia for more than two decades, compromising US intelligence at the highest levels. I was the undercover operative assigned to stop him. Working inside FBI headquarters, I became Hanssen's assistant in name, while secretly gathering the evidence that would lead to his arrest. That operation became the basis of my book Gray Day and the film Breach, in which Ryan Phillippe portrayed me. Since then, my path has evolved.