Here are a example for a .htaccess.
# Block Semalt related referrer spam
RewriteEngine on
RewriteCond %{HTTP_REFERER} ^https://.*youtubedownload\.org/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*simple-share-buttons\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*softomix\.ru/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*zazagames\.org/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*youtubedownload\.org/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*vapmedia\.org/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*soundfrost\.org/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*joingames\.org/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*videofrost\.net/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*softomix\.net/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*feedouble\.net/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*backgroundpictures\.net/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*joinandplay\.me/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*videofrost\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*srecorder\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*softomix\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*openmediasoft\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*openfrost\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*myprintscreen\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*musicprojectfoundation\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*feedouble\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*fbfreegifts\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*extener\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*embedle\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*savetubevideo\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*kambasoft\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} buttons\-for\-website\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*7makemoneyonline.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*semalt\.com/ [NC]
RewriteCond %{HTTP_REFERER} ^https://.*free-share-button\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*buy-cheap-online\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*best-seo-offer\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*Get-Free-Traffic-Now\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*buttons-for-your-website\.com/ [NC,OR]
RewriteCond %{HTTP_REFERER} ^https://.*torture\.ml/ [NC,OR]
RewriteRule ^(.*)$ – [F,L]
For more information
Best regards