The young students were recruited at Cambridge in the 1930s
As the BBC debuts a television series on the Cambridge spies, people now on the campus weigh in on the infamous alumni.
Former students Kim Philby, Donald Maclean, Guy Burgess, and Anthony Blunt were not motivated by money but believed in the anti-capitalist model of the Soviet Union.
Thy eventually moved into jobs in the establishment - working in the Foreign Office and British Intelligence, where they learned official secrets and passed them to their spymasters in Moscow.
Edward Cumming, President of the Cambridge Union, said: "As long as you don't get found out, it's probably very exciting.
"But I think to do it you've got to be something of a flawed character yourself - there's got to be a twin dimension to your brain and your mind."
The series was filmed in England and Spain
Professor Chris Andrew, a historian at Cambridge, told BBC Look East that the spies had thought themselves to be clever and admirable, but were mistaken.
He said: "They all began as idealists, but when they'd realised they'd made a mistake, they refused to admit it.
"So, one begins by having respect for them, but one ends by having nothing but contempt for them."
Three of the spies eventually ended up in Russia, while the remaining spy, art historian Anthony Blunt, was stripped of his academic honours and knighthood in 1979 when the full story of his involvement was revealed.
A "fifth man" connected to the spy ring, John Cairncross, is not depicted in the series.
Cambridge Spies begins on Friday at 2100 BST on BBC One.