In years past, security threats came from geniuses or nerdy students with lots of time. The numbers of these people were relatively small. Their main motivation was to prove that they could break into another network. Since then, the number of potential attackers and the sophistication of the attacks have increased exponentially. Attacks that once required attackers to have an advanced degree in computing now can be done with easily downloaded and freely available tools that the average junior-high student can figure out how to use. Every company and almost every person connects to the Internet, making essentially the whole world vulnerable to attack.
The biggest danger today may be the changes in attacker’s motivation. Instead of looking for a challenge, or to steal millions, today’s attackers can be much more organized and motivated. Organized crime tries to steal billions by extorting companies by threatening a denial of service (DoS) attack on the companies’ public web servers. Or they steal identity and credit card information for sometimes hundreds of thousands of people with one sophisticated attack. Attacks might come from nation-states or terrorists. Not only might they attack military and government networks, but they might try to disrupt infrastructure services for utilities and transportation and cripple economies. Security is clearly a big issue, and one that requires serious attention.
To appreciate a bit more about the dangers inside the Enterprise network, it helps to understand a bit more about the kinds of attacks that might occur:
 Denial of service (DoS) attacks: An attack whose purpose is to break things. DoS attacks called destroyers try to harm the hosts, erasing data and software. DoS attacks called crashers cause harm by causing hosts to fail or causing the machine to no longer be able to connect to the network. Also, DoS attacks called