The proxy server then substitutes its own computer identification for the internal user's computer. When responses are received, the proxy server determines which local computer is the recipient and forwards the response to it. Any crackers who monitor network traffic see only the identification for the proxy server. By installing these devices and diligently monitoring access attempts, an organization will repel most attempts to break into its network. However, preventing unauthorized access to network resources from the outside solves only half of the problem.
Unauthorized access can occur from inside the organization's walls as well.
And most anecdotal evidence indicates that threats of electronic theft or sabotage are greater from employees and individuals inside the organization than from persons outside. Disgruntled employees are a common source of unauthorized access. The first defense against undesired access to data resources is the implementation of user authentication. Authentication techniques get more sophisticated as the computer industry matures. Here are some of the means employed to make sure users are who they say they are.