These are usually Karmic issues where the Universe is 'thanking you' for every time you hit 'view source' on someone else's page for a little "inspiration" - or grabbed a gif, or downloaded an mp3.
Or something like that...
Seriously, one of my best selling sites is actually some fucktard's
stolen copy of one of my worst selling sites. While he may be better at sending traffic to "his" copy of it than I am to mine, he was not so good at replacing MY link codes with his!
