How to delete "semalt.com" visits from database? (no replies)

Hi at all,

I have now updated to the newest Version of piwik, so the Referrer Spam shall not be shown in my statistics from now.

But how I get rid of the whole spam entries from the last year of "semalt.com", "Buttons-for-sour-website.com" in my database?
Is there a SQL Statement which I can enter in my phpmyadmin?

Thanks for your help.