This has been asked a few times, but there's never been, as far as I can tell, a comprehensive and well-sourced answer. So, I encourage people to provide one.

That said, there have been good answers. Here's one with some good debate about what McCarthy got right or wrong, and another that discusses whether the "Venona Files" exonerated McCarthy's claim that communist inflitration was widespread and dangerous. (The answer given in the thread is "no" -- infiltration was real, but McCarthy didn't find it, and it was not the clear and present danger he believed it to be.)

I can't speak to the accuracy of those answers but if you don't hear back from others, that's a start.