Referral spam can seriously mess with your data in Google Analytics.
Using the filter function can block spammy domains and improve the accuracy of your stats.
- Edit the View for the website (Property) in question
- Create a New Filter
- Set Filter Type to Custom
- Set to Exclude
- Select filter field to Referral
- Create regex expression to filter those spammy domains
Here is an example of such regex based on spam referrals in the data for one of our own sites