EVER SEEN THOSE POP-UPS that tell you that your computer is hopelessly infected and that you should download a virus and spyware-busting program to clean your machine up? Well, in fact, by pressing "Okay" you will be doing just the opposite. Once you click that "Okay" button, the owner of the website will get a cut from the spyware company for scaring you into infecting your machine. Wouldn't you rather be that website's owner, rather than an ignorant sucker, who just allowed his computer to be infected?
Spyware does a bunch of potentially lucrative things for its owners: it collects your personal information, which can be simply sold, or used to serve you hard-to-kill pop-up ads or even can be passed on to certain people, who just might buy themselves very expensive toys using your credit card numbers. Of course, you will take no part in those shady activities - all you will do is provide a website convincing enough so that suckers... er, visitors will download the stuff.
Well, if conscience later gets the best of you, you could atone for your sins by creating a website that would link to legitimate anti-virus programs - a lot of these firms will pay you a referral fee for every sale, if you become their affiliate and direct customers to their software.