As of now semalt.com is blocked from Redistats and you won't get more hits from them.
Semalt.com is allegedly been using a tactic called referer spamming to make it look like you get visitors from these type of pages:
semalt.com/crawler.php?u=yourdomain.com
Redistats want you only to see human visitors and we have now blocked this large scale spam.
If you are operating a website with a large number of subdomains I urge you to also block this bot at the server level in order to save resources.
With .htaccess in Apache:
# block visitors referred from semalt.com
RewriteEngine on
RewriteCond %{HTTP_REFERER} semalt.com [NC]
RewriteRule .* - [F]
Nginx:
if ($http_referer ~* (semalt.com))
{ return 403; }