Intrusion detectors can spot an attack in real-time. And now, a final point. VPNs are a wonderful tool for providing private network-like access over a public network. Today, most VPNs require an a priori relationship between user and server. Although many users may not have not used a VPN to connect back to their corporate network, most have used a form of VPNs on the Internet.
Certificates provide a trusted way to bind a user identity and a public key.
Within a few years, I believe that individual certificates will become commonplace, allowing users the ability to access many new services, both public and private. These musings don't even begin to scratch the surface of network security issues, but I hope that they make you think about the importance of this problem. Gary C. Kessler is a frequent speaker at industry events in and out of Vermont.