A firewall is defined as a security system that prevents outside users from accessing private network resources. They can be set up between segments of a network, but are usually used to improve security between the internet and a network.
In order to understand the concept, it is useful to think of a castle with a mote dug around it. All traffic into and out of the castle, is thus forced to pass over the single drawbridge. The drawbridge is like the firewall (See diagram 1).
Although there may be an actual firewall between the internal network, and the Internet, the virus can be spread once a computer (this may be for example, a laptop brought onto the network) on the internal network becomes infected. It then propagates itself, without user help. Results in the shutdown message shown below.
There is a tendency among local businesses to overlook the importance of security. These business generally adopt the attitude that it ‘couldn’t happen to them’. On Wednesday, September 22 nd , 2004, the nation newspaper company, and the Starcom Network Company were both proven wrong in this belief as both their websites were hacked.(nationnews.com, vob929.com)
The screenshot below shows the contents of the nation website on the day in question.