When I founded my business a whistle-blowing-service for enterprises, I’ve seeked for a working solution to block spam bots on that home page. The solution was intended to comply with EU data privacy law, no cookies, no sniffing, light-weight-size, on my webserver only, beeing invisible for my site visitors and no running costs at all. I came across Hashcash, a proof-of-work approach, to block spam. When I implemented it, it worked immediately and blocked 100 percent without blocking any incomin...