What to think of this?
There are two books you can read. One is old from the time, the other is more recent.
Buckley and Bozell wrote a book (before Buckley became a sellout). I used to own it but I lent it out and don't know where it is now.
And recently a book has been published "Blacklisted by History" - which I own.
They are rather detailed.
I recommend you read up on the Silvermaster Spy Ring and Elizabeth Bentley, etc.