Content Filter Technology
Content-control software, also known as censorware or web filtering software, is a term for software designed and optimized for controlling what content is permitted to a reader, especially when it is used to restrict material delivered over the Web. Content-control software determines what content will be available.
The restrictions can be applied at various levels: a government can attempt to apply them nationwide (see internet censorship), or they can, e.g., be applied by an ISP to its clients, by an employer to its personnel, by a school to its students, by a library to its visitors, by a parent to a child’s computer, or by an individual user to his or her own computer.
The motive is often to prevent persons from viewing content which the computer’s owner(s) or other authorities may consider objectionable; when imposed without the consent of the user, content control can constitute censorship. Some content-control software includes time control functions that empowers parents to set the amount of time that child may spend accessing the Internet or playing games or other computer activities.
In some countries, such software is ubiquitous. In Cuba, if computer user types a dissent keyword, the word processor or browser is automatically closed, and a “state security” warning is given.
Filters can be implemented in many different ways: by a software program on a personal computer or by servers providing Internet access. Choosing an Internet service provider (ISP) that blocks objectionable material before it enters the home can help parents who worry about their children viewing objectionable content
Gateway-based content-control solutions
Gateway Based Content Control Solutions may be more difficult to bypass than desktop software solutions, since they are less easily removed or disabled by the local user.
Content filtering technology exists in two form: Proxy and Passive. Proxy based solutions have several benefits and shortcoming. Proxy based solutions offer detailed rules based configuration at the price of performance and simplicity. Proxy technology prevents traffic from continuing to the targeted destination until inspection has occurred and deemed acceptable. As points of failure investment in hardware can be significant to ensure quality of service as rules are added. The more rules defined the more inspection that occurs requiring administrators to balance cost to performance. Passive solutions differ in that they are by-pass or side scan filters leveraging signatures. Passive technology allows packets to pass the filter to the destination. Inspection terminates the tariff by using TCPIP resets for HTTP protocol and application level knowledge for peering protocols. Signature escalation enables passive solutions high performance at a significantly lower total ‘cost to performance’ ratio.