Historical perspective can be very educational.
The British Broadcasting Company has recently found a film of British spy Harold “Kim” Philby giving a how-to class to the East German Ministry for State Security (MfS or StaSi). after his defection to the Soviet Union. The linked film excerpt lasts about 3-1/2 minutes and is worth watching and hearing.
The newly-found film is noteworthy not for any clever spy tradecraft it reveals but how easily Philby “…got away with treachery…” because he had been “… born into the British upper class.” Exposing someone of his social and political prominence would have caused a scandal in Britain.
Philby reveals how at night before he left work, he simply crammed his briefcase full of secret material, left the building, delivered the material to his case officer/handler who then photographed it. The next morning, Philby retrieved the secrets from his case officer/handler and returned them to the office with no one the wiser.
If Philby were to be resurrected and reactivated today, his briefcase might conveniently be replaced by a private email server.
“Those who cannot remember the past are condemned to repeat it.” (George Santayana, The Life of Reason, Volume 1, 1905)