All ports were open to the world and practically every application had holes in it. It was like the Wild West. Eventually application security became a big deal as more serious issues were uncovered and more commerce depended upon secure platforms. Network security was next on the scene. It made sense to build a single choke point for all security needs. It was slick because it could see all the packets in transit to and from your servers, and turn off all access to anything that had a known hole in it. Those were the good times. Times have since changed.
Network security, in large part, had a huge role to play in creating the newest attacks. Network administrators rightly told their architects to build applications that could be tunneled over hypertext transfer protocol, while at the same time they would close down all access to any other unnecessary inbound services. Can you see the obvious flaw in their logic here? Even still, aside from the occasional hole in IMAP or BIND, the world of computer security seemed to be calming down quite a bit with the advent of stateful packet inspection and security information management tools. Most of the holes at that time were against the security tools themselves, which most of the hardcore security folks felt was scraping the bottom of the barrel -- the last bunch of entry points to a secured network.
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