Internet Filtering basics
By Alex Polling

Our body is made so that it perceives (filters) only certain kinds of information. For example, our eyes detect photons of wavelength between 400 and 700 nanometers, and everything out of this range passes by us, remaining undetectable. In that way, we can’t hear some sounds that can be heard by animals or using special equipment. The process of evolution selected these kinds of information as the most important for our survival, and everything else is filtered out.

But with the Internet things are a bit different. It has grown too fast and we do our best trying to cope with large amounts of information, most of which we may not need at all. And what’s more important, there is a lot of information that contains offensive, "inappropriate," or "objectionable" material. This material can fall into different categories, but the point is that we need to filter it out using filtering software, as we want to enjoy using the Internet and to feel safe about our kids enjoying it. A filter is a kind of software program that prevents one from viewing objectionable material on the Internet.

Actually, filtering software does two things.
The first thing it does is it rates or categorizes web sites using different kinds of distinctions and algorithms.

Second, based on the security level of the current user, it decides whether to block the requested material or not.

There are a few kinds/features of filtering.
URL filtering. Blocks URLs containing inappropriate or blacklisted words.

Keyword blocking. The software uses a predefined list of keywords that it considers offensive or inappropriate. Before the requested material is passed to a user, the software searches it for any of the keywords from the list and blocks the content.

Web-sites blocking. Blocks entire web-sites or some parts of these web-sites based on a blacklist (list of blocked sites) drawn up by companies. Most software vendors do not allow their users to see the list of blocked sites, they consider it a secret but you can add new or exclude existing sites from their list.

Protocol blocking. Since we use not only the web, but also Instant Messaging or newsgroups, filters provide IM blocking, FTP blocking, email blocking, and Peer-to-Peer (P2P) blocking.
Dynamic Categorization. Uses smart algorithms to decide whether the content is appropriate or not based on the content of web page. This kind of categorization is smarter than keyword blocking, which may filter out totally appropriate content containing objectionable keywords in an appropriate context.

Image Recognition. Filters inappropriate graphical images. Filtering of inappropriate graphical images requires a lot of computer time and because of this it is mostly not used in today’s filters.

Newsgroup filtering. There can be simple newsgroup filters which block access to all or specific newsgroups, but more flexible filters like CyberSieve allow you to restrict specific users to specific groups or even to groups that fall into some “group pattern”.

These are basics things that filtering software does.

In addition there are features that make filtering software much more convenient and user friendly. One of them is the e-mail notification system. For instance, the notification system of CyberSieve will send you e-mail messages when any banned web site has been visited thus allowing you to take action immediately. Also in CyberSieve you can specify the programs that can or cannot access the Internet. For example, you can block Internet access for peer-to-peer program and allow Internet access for your email client. And it is also possible to restrict specific users to only a few specified programs that require Internet access. The latter makes CyberSieve a truly family solution because each user can be given specific restrictions and privileges tailored to his or her age and needs etc.

One more useful feature of CyberSieve is that not only users/groups can have different levels of access, but you can also set limitations on Internet traffic (the amount of data that can be sent or received.) The access to the Internet can be scheduled to specify days and times.

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