Eventually, the criminal will probably break into one of the vulnerable places and commit some offense. But on the scale of the Internet, we're talking about thousands upon thousands of doors, which means that your computer is unlikely to be singled out for mayhem. Without a personal firewall, your door is wide open. By blocking all such unauthorized access to your computer from outside, a personal firewall represents adequate protection for most users, Gibson said. Like the corporate type, a personal firewall can be configured with varying levels of filtering, letting in all, some or none of the traffic coming in on various ports.
Most end users are probably best off blocking most traffic, although there are exceptions.
For example, in the case of corporate remote access, certain IP addresses assigned to the enterprise might be allowed to transmit through the firewall. Much like the early Netscape business model, Zone Labs plans to make money by selling centralized management software to businesses that can configure the personal firewalls consistently across the enterprise. King and Gibson believe that personal firewall functionality eventually will be built into other products and simply become a transparent part of any system for always-on Internet connections. If your cable modem connection is part of a corporate data VPN, you get an added layer of protection, thanks to VPN encryption. You're on the 'Net, you've got a firewall, but you're not scaled up to spend tens of thousands of dollars.