At this point I believe that McAfee was talking only about the identification of "Guccifer 2.0" as a Russian - and not about the evidence that the Russians actually hacked the DNC. "Guccifer 2.0" released information from the hacks but does not have to be a member of either of the teams that actually extracted the information.
Some more, [url=www.bbc.co.uk/news/blogs-trending-38610402]
The evidence for the latter is rather better. Again, Crowdstrike, the FBI and the CIA all agree on the two groups responsible, identified by their methods.