This file is created to collect and prevent referral spam traffic sources.
Referral spam has been spread wide across the web. Add this to your .htaccess file on a Apache server to prevent referral spam traffic from websites like semalt & buttons-for-websites. This file is usually found in the root “public_html” folder of your website.
NOTE: This method doesn't stop the Analytics referral spam (because they are hitting Analytics directly and not even touching your website / server). You should also use filters in Analytics to prevent referral spam.
If this method fails you can prevent referral spam by:
If you'd like to help, just fork the repository, then add useful stuff and send a pull request.