The Soviet model of ideological fear was not about outsiders breaking into their society (they were a closed society, so not much chance of that — the US actually found it nearly impossible to embed Western agents into the USSR), but about subversion from within. So the Stalinist purges were about imagined groups that threatened the Soviet order, often by having an identity that was separate from a truly "Soviet" one, and by sabotaging ("wrecking") the Soviet project. So these identities could include all sorts of things, beyond the usual ones of the Kulaks (formerly wealthy peasants), various pan-Soviet ethnic and nationalist groups, and forms of Communist ideology that were deemed enemies (Trotskyites, Mensheviks, etc.), but also even included groups like engineers, who were seen as harboring a different sort of "class sensibility" that kept them from truly assimilating into the Soviet worldview. And there was no "blue scare" but there certainly were elements of a "White Scare," where White refers to the non-Communist forces of the Russian Revolution.

Which is to say, the parallel to McCarthyism in the USSR was Stalinism and the purges — paranoid and exaggerated fears that led to huge campaigns to root out the ideological enemy among them. It was, to be sure, considerably more brutal than McCarthyism, and had its own, separate dimensions (McCarthyism, for example, was never joined to an economy of forced labor — so there was no internal economic incentive for McCarthyism, whereas there was for Stalinism).

There are many books on the Soviet purges and the "Great Terror" of the 1930s. Though it has many issues and should not be taken as a straightforward "work of history," Solzhenitsyn's Gulag Archipelago goes into exquisite detail on the architecture and ideology of the purges, and makes for fascinating reading.