Content filtering is a process whereby the type of content entering a computer is filtered. Usually, this involves installing a piece of equipment in your network, or software on your device. All websites pass through the web filter before displaying on the screen. If the website isn’t listed in the web filter as restricted, it can be viewed. If the website is restricted, then the user won’t be able of view it.
There are other types of content filters. For example, a specific category may be restricted. The best example of this is adult content. The entertainment category may be restricted as well.
Sometimes, content may be blocked, even if it isn’t in one of these restricted categories. But this is accepted in the name of security. Most businesses and organizations prefer secure Internet access, rather than an open Internet. The biggest concern is computer viruses, malware, and other types of destructive applications. The ultimate goal is to prevent damage to their computer systems. By restricting access to sites that have an unknown category or rating it is often easier to catch malware before the user realises.
Another area of concern is email. Attachments in emails are a source of computer viruses. Some content filters screen email content, which is an invaluable service when there’s a new computer virus making its way around the web.
Here’s a list of other types of content filters:
Client-side filters – Each computer in an organization contains software that filters the Internet. This software is installed by the administrator, and the administrator can disable or uninstall the software.
Content-limited ISPs – The Internet service provider limits access to the Internet. Only a set portion of content is accessible in this type of connection. The user usually accepts the condition, especially if the purpose of the filtering is to comply with government or parental restrictions.
Network-based filtering – There are two types of content filtering at the network level. It can take place at the transport layer (transparent proxy) or the application layer (web proxy). It is usually used to implement different levels of filtering for different institutions (high school vs middle school).
Search-engine filtering – Most search engines have a safety filter that prevents inappropriate websites from being listed on the results page. Some search engines have a children’s version that only finds child-friendly websites.
There are two types of content filtering products that security vendors may offer. Application gateway and packet inspection. The application gateway is usually a web-proxy. It can review the request by the user and the webpages that are returned. The proxy can make substitutions to the results. An example of an application gateway would be a Sophos XG Series Firewall.
Packet inspection filters don’t interfere with the connection to the server initially, but they do so after inspecting the data. If the content is deemed to be filtered, the connection is blocked. This is done with a TCP-Reset, which is considered a fake packet.
Some security vendors may offer a content filter that combines both methods. This is popular since it reduces the overall cost of the system.