A large number of websites, both legal and illegal, that can be freely accessed online have content that is malicious, inappropriate, prohibited or bad for productivity. Accessing malicious websites may result in the installation of malicious codes without the user’s knowledge. The organisation may also be held liable for access to prohibited or illegal content.
To prevent employees accessing such websites, the organisation can install a web filter as a means of protection.
In technical terms, these filters are called “web proxies” and can take several forms. The best-known free proxies are “squid and squidguard”, “DansGuardian” and “HAVP”, which can be found in a large number of free or paid firewall products.
A web filter analyses all communications (content and/or recipients) to and from the Internet to detect exchanges with sites hosting malicious, inappropriate or prohibited content. This filter is not to be confused with the browser’s phishing filter, because unlike the latter, which is installed in the user’s browser, the web filter runs on a dedicated server and cannot be easily circumnavigated by the user.
A web filter that analyses URLs has a database that links URLs with content categories. These databases are managed by specialised companies who associate the websites with various categories, such as pornography, gaming, gambling, and so on.
Once a new website has been discovered, it is categorised and, if necessary, added to the database. This type of filter does not prevent access to brand new websites that haven’t yet been categorised or access to websites that have only recently become malicious.
The organisation can nevertheless filter different content categories, such as pornography, gambling, social networks, etc.
Some web filters are able to analyse the content of a website a user wants to visit. Based on a list of key words, the filter allocates a category to the websites visited and either displays or doesn’t display the requested content. This filter is useful for preventing access to recent content for which the URL analysis wouldn’t have worked, but can also generate a lot of false positives.
Some filters contain antivirus programs and can analyse the content of websites visited and block access to potentially malicious software.
Some web filters can analyse the requested images. The filter selects the images on the website visited and allocates them to a category before displaying or not displaying the content.
Draw up and enforce the following sectoral policies: