There is a bot going around poisoning thousands of Google Analytics data with referral spam for semalt. As far as I can tell this is a pointless service. There is a useful blog posts on how to block it using htaccess. The problem is it can upset your referral reporting and bounce rate.
iIf you are unable to block using htaccess still want to remove it from your Google Analytics it is fairly simple. While viewing your statistics click Admin then Filters. You want to create a new Custom filter with the details set as per my screenshot. This should then stop reporting on any referral traffic from semalt. Existing data will remain but future reports should no longer contain it.