Kim Philby was one of the most notorious double agents Britain ever produced - for three decades he secretly worked for the Soviet Union, passing it secrets, whilst sitting at the heart of MI6, the UK's Secret Intelligence Service.
When his cover was blown in 1963, Philby defected to the Soviet Union, and died in Moscow in 1988.
BBC News has now uncovered a previously-unseen video recording of Philby giving a lecture to East German Stasi agents in 1981, describing how for years he walked out of his office with a briefcase stuffed with secret papers.
Snippets of the video have been released online.
“Every evening I left the office with a big briefcase full of reports which I had written myself, full of files taken out of the actual documents, out of the actual archives. I was to hand them to my Soviet contact in the evening. The next morning I would get the file back, the contents having been photographed, and take them back early in the morning and put the files back in their place."
Furthermore, Philby explains that he believes he avoided suspicion because of his upper-class background.
Time and technology have moved in on the intervening years, but the threat posed by insiders within your organisation remains real.
Many security vendors and media focus on the threats of external hackers, malware attacks and the like - whilst turning a blind eye to the risk that you may have a rogue employee on your payroll, surreptitiously stealing information and causing harm to your business.
The reason for the focus on external threats is easy to understand - they are easier to stop. Preventing someone who you have invited into your organisation from stealing information and secrets can be a lot harder than stopping a remote hacker.
But don't make the mistake of ignoring the insider threat. It may be harder to control, but the damage that can be caused by a spy in your midst can be considerable.