Semalt have annoyed many webmasters by skewing analytics as their crawler turns up as a referrer. To add insult to injury, the Semalt crawler does not honour robots.txt nor does using the Semalt removal tool do anything more than invite further bot visits.
This pdf outlines 3 ways you can stop Semalt from polluting your analytics:
1. Block the Semalt crawlers via htaccess
2. Block Semalt crawlers via php
3. Remove Semalt referrals via Google Analytics