Are you interested in selling a product retail, making a product and wholesaling it, or offering a service?
You could offer security consulting services. Given your experience, that would seem to be a fairly obvious choice. Only thing is, if I were going into that sort of business, I'd want to make sure I had tons of liability insurance, because all it would take is one client who followed my advice and got hacked anyway and I could find myself in court.
Aside from that, the field is wide open. What sorts of things are you interested in? What do you do when you have free time and can spend it any way you want? What sort of resources do you have available (cash on hand, skills, business relationships, raw materials, etc.)? Can you identify any unmet demands or needs in your area? That is, things people want to buy, but can't find in stores, services they need but nobody offers, etc.
There are as many different potential businesses out there as there are would-be entrepreneurs. Nobody else can tell you definitively what will be a good business for you based on a one-paragraph forum post. You need to think about what people want/need and what you have to offer that can help them meet those wants/needs.
Diane Aull - NineYards.com
: Helping Businesses Do Business Online
Whether you think you can, or that you can't, you are usually right.