I obviously didn't spend enough time to think about it hard enough and wasn't able explore the good sides of advertising. I had a web app and placed a big banner over it, the banner often seemed to show confusing buttons like "SHOW" or "DOWNLOAD" and I guess the users then accidentially clicked it. I think the main problem was that there were no ads that fit to the app (it was a QR encoder/decoder) so I wasn't able to provide a positive ux. Do you have any tips on how to find the best fitting ads for (sometimes very technical related) specific sites/apps?