Several years after his death, it was revealed that since the late 1950s he had been an agent of the Stasi, the State Security Service of the German Democratic Republic.
There in the late 1950s he undertook to cooperate with the East German Main Directorate for Reconnaissance, and was released early from prison on 28 August 1959.
[4] He met regularly with the head of the Foreign Intelligence Markus Wolf and case officers in East Germany.
[5] According to Stasi Lieutenant Colonel Günter Bohnsack, the GDR's intelligence services wrote many of Borm's parliamentary speeches and articles in the 1960s.
Politically Borm began to push for an agreement with the GDR, and in 1963 he published a controversial plan called "Germany".
In 1981 he became involved in public for the peace movement against the NATO Double-Track Decision, and on 10 October he spoke in front of 250,000 people in Bonner Hofgarten.
In the same year he opposed foreign minister Hans-Dietrich Genscher, accusing him of working towards the final goal of German reunification, undermining the policy of European détente.
However, in 1979, Borm explained in a secret conversation with the head of the Western Department of the Central Committee of the SED Herbert Häber that the idea of socialism was correct.
His gentlemanly appearance earned him the nickname "Sir William" from friends and from the head of the East German foreign espionage.