I've been getting these random suggestions and ads online from "CryptoTab". It's a Google Chrome and Firefox extension that mines bitcoin in the background of your browser. "Invite your active friends who will invite their friends". My take on this is that one will not become wealthy from this overnight at all, and could take months to make a couple of dollars. Mining BTC on a PC sounds ridiculous and more of a pyramid scheme here. I doubt anyone will break-even with electricity bills at all, even with multiple referrals.