Stalin's purges had absolutely nothing with removing any "5th Column." The White Movement was thoroughly defeated by 1921 as were the Mensheviks etc. Stalin purged his officer class because he was supremely paranoid. And while he killed many of the officers, many were sent to the gulags and recalled to service after the German invasion in 1941.

The entire concept of a 5th column is just fear-mongering by most countries who faced defeat due to their incompetence. And the term was used by countries to impose draconian controls and oppression.