What is Filtering?


Internet filters are programs that block access to resources considered inappropriate for a particular audience. Most often, filters are used to prevent children from accessing sexually-explicit websites. However, filters can also be used by businesses needing to restrict staff access to entertainment sites, such as sports, movies, chatrooms, etc.

How do Filters work?

There are two main types of filters. Keyword matching filters rely on pre-defined lists of objectionable terms. Access to a website is blocked if it contains one or more of those terms. Alternatively, the offending term or a portion of the page that contains it may be obscured or altogether deleted. The disadvantage of this method is that depending on the context, a particular word or phrase may have a totally innocent meaning.

Another option is to use site blocking filters, which consult lists of sites deemed inappropriate by human reviewers. Access can be blocked to complete websites, or to certain areas or pages inside a website. Given the constant growth of the Internet, these lists can never be comprehensive, nor can they cover all areas of concern (such as violence or crude language) equally. Thus, it is desirable that a blocking product allows some customization of its site lists.

Does filtering infringe on our First Amendment rights?

The American Library Association (ALA) strongly supports free access to Internet resources. ALA's Resolution on the Use of Internet Filters states that "the use of filtering software by libraries to block access to constitutionally protected speech violates the Library Bill of Rights." On the other hand, organizations like Filtering Facts work to "protect children from the harmful effects of pornography by promoting the use of filtering software in libraries."

Libraries are caught in the middle of this controversy, and setting adequate access policies can be challenging. In Texas, the Penal Code (Ch. 43, section 24) prohibits the display of "harmful material" to individuals younger than 18 years. Based on this law, the Austin Public Library (APL) decided to install filtering software on all of their Internet workstations. However, after public pressure built up, and in consultation with community groups, unfiltered stations were added for the use of adults. Special tables that keep the display hidden from public view were designed and installed. See the APL's Internet Access at the Austin Public Library open letter.

What filtering products are available?

If an institution decides to implement filtering, several vendors should be contacted for current information. Some well-known filtering products include: CyberPatrol, CyberSitter, NetNanny, SafeSurf, and SurfWatch. For a list of vendors and contact information, please see the TSLAC Filtering Software Packages page. Before purchasing a filtering package, ask vendors to provide you with a trial version of their product. Install and test each product to make sure it meets your needs! The Internet Filter Assessment Project (TIFAP) lists filtering products and provides assessment tips.

return to top

Page last modified: March 2, 2011