Content-control software, also known as censor ware 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 on a particular machine or network; 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. Common use cases of such software include parents who wish to limit what sites their children may view from home computers, schools performing the same function with regard to computers found at school, and parents restricting what content may be viewed by children's.

Parental controls are options, typically included in digital television services, computer and video games, or computer software used to access the Internet, that allows a parent to monitor or limit what a child can see or do and/or time-limit these activities. These controls may allow for the blocking of television stations using V-Chip technology, the removal of gore from computer games, the blocking of various websites, such as those containing pornography, or the automatic censoring of swearing.

Several technologies exist in creating parental controls for blocking websites. The API method uses the operating-system programming interface to gather information about a foreign application such as browsers and chat applications to seize control of the foreign application when the information gathered triggers a positive in a database of banned words. Parental control software using API technology is limited to shutting down the offending application; in some cases, a different action like deleting the offending words may be possible depending on how the offending application is programmed.

The next widely utilized technology is the proxy server method. An application such as a browser will communicate with the proxy server and the proxy server will then handle the request and fetch the Web page and return it to the browser. This helps security because the workstation never deals directly with the foreign server but only with the proxy, which can also speed up the connection and alleviate congestion by caching content locally.

Another way security is improved with proxy servers is to inspect the data being sent and received; if by rules of definitions the data is tagged bad, then the proxy server can act like a firewall and deny the communication. In this example the proxy server is an http proxy and receives an http header request for a Web page; the server will parse the host section or the get section of the header and do a search in a database of banned (user-defined) words or banned (user-defined) URLs. If there is a positive match the proxy server never relays the request to the remote server, but instead either returns nothing or leaves the response to the local client application to deal with, or returns an alternative response to the request, such as a custom "denied" page or a redirection header.