Bust the Ghost in the Machine: Referral Spam
Have you noticed a surge in referral visits to your website lately? When you try to track them down, does it only lead to confusion? Maybe you've gotten a warning about self-referrals from a domain you don't even own. The culprit is none other than referral spam.
What is referral spam and how does it work?
Essentially, a website will find a domain (possibly yours) that uses a public analytics platform. Then, they will send fake visits to your website. Then, the analytics platform will record it as a referral and provide a link back to that website. Shady stuff.
Why is this bad for you?
Your referral data is inaccurate! You're looking at more traffic than you're actually getting and if you're unaware of the referral spam, you may make a poor decision as a result.
How to fix it
The best way is using a hostname filter. Alternately, you can filter your traffic (in Google Analytics anyway) so this doesn't appear. It is a less accurate fix, but it will let you see more accurate data with fairly low effort.