Is Your Client’s Network WIDE OPEN!!!

Recently I had the opportunity to work for a company who was on a Cable Modem network. Unfortunately they were getting the Sircam virus over and over again. Fortunately I stepped in and identified the problem. Their network was open to everyone witha cable modem in their neighborhood (from one block to 5 miles away). I fixed the problem and successfully identified four companies in the network that were WIDE OPEN. My question . . . . . how would I approach these companies with this security concern? What would you do if you could help a company and potentially gain a client for yourself?