Awhile back I had the idea to make an anti virus product that worked as a proxy server. Unlike quite a few of my ideas, this one actually made it all the way through to production.
What prompted me was some value priced radio advertising I purchased. I realized I didn't have any products to sell to the consumer market, so I looked back in my pile o' ideas and pulled out the first one I though I might be able to get done before the radio adds aired.
In the end, my revenue projections were a bit too optimistic and the whole thing used a bit too much bandwidth to be worth the advertising money I got from it, so its been shutdown for awhile now.
However, the firm I'm at right now has a program for ISVs to sell software running on there boxes. So, I'm going to dust it off, re-package it (so it runs on there boxes insted of my central server) and see if I can convince anyone that its a good idea to "Stop viruses before they get to your computer".