The whole meaning of networking is to share programs, but granting others to access a computer device reveals an open window for those with foul motives, too. In the early days networks were quite secure because they were closed in systems, and to do any harm you had to get physical access to a server wired to the LAN. Remote access and Internet possibility to hook up has changed that. Broader availableness and less cost of broadband (DSL and cable) connections means that even home computers remain linked up to the Internet round-the-clock, which add the chances for hackers to gain access to computers.

Computer operating systems were originally planned for stand-alone computers only, not networked ones, and security was not an issue. When computer networking became known, applications and operating systems concentrated on easy accessibility rather than security. Because of this earlier focus on accessibility; security are now retrofitted into a lot of hardware systems. Modern operating systems such as Windows XP are planned with security in mind, but they still have to operate using conventional networking protocols, which can result in security problems.

Security versus access. The users want easy access to network resources. Administrators want to remain the network secure. These two goals are at odds, because access and security are always on conflicting ends of the scale; the more you have of one, the less you have of the other.

For business computer networks, the key is to hit a balance so that employees are not annoyed by security measures, while trying to maintain a level of protection that will keep unauthorized individuals from getting access.

Internal network security threats are those that come from within the organization, as opposed to those that come through the Internet. Internal threats include employees who on purpose attempt to nick data or bring in viruses or attacks on the computer network. Other internal threats are posed by outside employees (contract workers, janitorial services and people posing as utility company employees) who have physical access to the LAN computers. Though, many internal threats are unintended. Employees may install or use their own software or hardware for a private purpose, unaware that it poses a security threat to their computers and the complete network.

External security threats are those that come from outside the LAN, typically from the Internet. These threats are the ones we usually think of when we talk about hackers and computer network attacks. Such people can make use of flaws and characteristics of computer operating systems and software applications. They take advantage of the way various network communications protocols work to do a range of things, including the following:

Enter a system and access (read, copy, change or delete) its data.

Break down a system and harm or destroy operating system and application files so they do not work anymore.

Install virus and worms that can spread to other systems across the LAN.

Or use the system to start attacks against other systems or other network.