Spam and ghost referrers appearing in Google Analytics has been a major issue for some time. Your stats will be biased to some degree if there are lots of spam referrers.
If you want to know more about this and how complex it is to resolve, have a look at the article at http://help.analyticsedge.com/spam-filter/definitive-guide-to-removing-google-analytics-spam/
The first part of the article tells you about the issue in reasonably readable terms Continue reading


