I met a guy once who made a browser add on that had legitimate functionality that people wanted, but behind the scenes he secretly read all incoming html and searched for Google Adsense links and replaced the number that identifies the source site with the number for his own site that had Adsense on it. So, whenever anyone with his add-on clicked any ad on any website with Adsense he would get credit for it and earn the money from it. They were all legitimate clicks so it was essentially impossible for Google to detect. He was getting several thousand a month in income from this. Haven't spoken to him in a while so I'm not sure if it still works of if people even still use his add-on. My guess is that either his add-on became unpopular over time or some changes Google made killed his nefarious plan.

I keep telling my other friend it would be really great if we could get a botnet going to mine Ethereum via GPU since ASIC mining isn't a thing in Ethereum because of it's resistance to it. Although, if they ever roll out the proof of stake concept then all mining seems to just evaporate then. Of course I don't plan on risking felony charges to mine Ethereum, but it is fun to think about.