Most web filtering companies use an internet-wide crawling robot that assesses the likelihood that a content is a certain type.
The resultant database is then corrected by manual labor based on complaints or known flaws in the content-matching algorithms.
A content filtering proxy will often support user authentication to control web access.
It also usually produces logs, either to give detailed information about the URLs accessed by specific users, or to monitor bandwidth usage statistics.
Ironically, websites commonly used by students to circumvent filters and access blocked content often include a proxy, from which the user can then access the websites that the filter is trying to block.
In such situations, proxy analysis of the contents of a SSL/TLS transaction becomes possible.Communication between two computers (shown in grey) connected through a third computer (shown in red) acting as a proxy.Bob does not know to whom the information is going, which is why proxies can be used to protect privacy.The SSL/TLS chain-of-trust relies on trusted root certificate authorities.In a workplace setting where the client is managed by the organization, trust might be granted to a root certificate whose private key is known to the proxy.An anonymous open proxy allows users to conceal their IP address while browsing the Web or using other Internet services.There are varying degrees of anonymity however, as well as a number of methods of 'tricking' the client into revealing itself regardless of the proxy being used.It may also communicate to daemon-based and/or ICAP-based antivirus software to provide security against virus and other malware by scanning incoming content in real time before it enters the network.Many work places, schools and colleges restrict the web sites and online services that are accessible and available in their buildings. This is done either with a specialized proxy, called a content filter (both commercial and free products are available), or by using a cache-extension protocol such as ICAP, that allows plug-in extensions to an open caching architecture.Assuming the requested URL is acceptable, the content is then fetched by the proxy.At this point a dynamic filter may be applied on the return path.