Jetsli.de is pretty much the same kind of thing as semalt. Semalt would give me hits on my blogs seemingly originating from various countries. One time I had 1200 hits from Tel Aviv that were semalt. To the best of my knowlege, semalt is actually operated out of Ukraine by a gang of Ukrainian criminals.
Semalt tries to draw attention to itself by spamming blogs and on their home page offer analytics for a fee - the same analytics that can be obtained from Google absolutely free.
Jetsli was traced and that went back to a server that apparently houses about 22K spam domains and it's based in Germany. I did read somewhere that Jetsli was linked to pedophilia but I can't find that link now.
All these spam referrers do is try to get somebody to click on the link to investigate it then if the resultant page looks tempting enough, some people are silly enough to spend money on their site. Whether their card information is then sold on the Russian black market is unknown.
The only thing to do is just to ignore Jetsli. Eventually the spam referrals will get filtered out by Google etc and they'll stop showing up in the viewer figures.