A content filter is a program that is used to filter certain unwanted content (e.g. data, images, audio files, …) before it can pass from one network to another. That’s why a content filter is usually located at the interface to the input of the network and controls the data coming into the network before it can get into the network part accessible to the users.
These content filters are often used by businesses, governments, and organizations to identify specific content by characteristics and characteristics. So that this detected content can be blocked and excluded from one’s own network. The aim is to protect the users of a network from dangerous (e.g. terrorist propaganda) and illegal content (e.g. copyright infringements). It can also improve user productivity (e.g. less distraction) or increase the technical security of a network (e.g. against industrial espionage).
Features and Functions
A detailed filter makes it easier to control the content being viewed. Partly unnoticed by the user, this system blocks or filters, for example, websites or e-mails with regard to individual words, typical phrases, images or links. Content filters are part of the recommendations for the operation of secure mail servers.
---
In most cases, these areas are configured by means of a categorization, using lists (databases), such as the rejecting blacklist or a whitelist, which still allows access. Typical examples of predefined categories are pornography or right-wing extremism.
Simple Content Filters
Simple filters only check content based on certain selection criteria. The disadvantage of using very simple filters is that any page that contains certain “regular expressions” is blocked. Pages that use banned words in a different context can also be blocked. If, for example, the word “sex” is blocked in any form, not only will every page that uses this word in general – even in an innocuous context. Another simple method is to block specific ports or network protocols.
Intelligent Content Filters
To avoid the drawbacks of simple methods, intelligent filters work with weights and reject a page only when a certain relevance is exceeded. In addition, they also use heuristic methods and, in the case of e-mails, greylists.
An intelligent content filter, unlike a URL filter with a high probability of success, is able to correctly assess web pages or emails. URLs that are found to be good can also be cached for a certain amount of time to avoid time-consuming checks for repeated requests.
Restrictions
Simple filters can only check URLs, texts, and images that are classified according to certain standards. Text that is displayed in image form can only be checked if the filter also supports OCR text recognition. Of course, it is also only possible to keep “blacklists” of all unwanted sites to a limited extent.
Advanced systems also combine an antivirus program with the content filter to detect malware that has been introduced via this system, for example via scripts or images.
As of 2014, content filters are often offered as a separate service for a fee; the service providers take care of updating the filter lists and the intelligent filtering according to configurable criteria. There are significant costs per year per Internet user.
