semalt.com is a known domain used in a Referer stats phishing scam. The goal is to get you click on the referer link in your stats for probably 2 reasons. Increased traffic to semalt.com and the possibility that you will buy their SEO services.
http://wordpress.org/support/topic/advise-1/page/2#post-5129764
If you have a stat counter plugin that is still logging the semalt.com domain in your stats you can wrap your stats counter code in this conditional wrap so that the semalt.com Referer will no longer be logged in your stats.
<?php if ( !preg_match('/semalt\.com/', $_SERVER['HTTP_REFERER']) ) { ?> // your statcounter code goes here <?php } ?>