I do not trust comscore's numbers at all. They rely on opt-in sampling of user data. There is obvious selection bias there. Large companies will never allow such tracking software, so anybody browsing from work will never be counted. There are many other large demographics that they just plain miss. They have a history of goofing badly, for example being directionally wrong about Google's ad revenue [1].

1. http://seekingalpha.com/article/72911-why-was-everyone-wrong...