Internet Filtering Methods

It is important to note that no filtering method is perfect. The web changes minute by minute. Web URLs are fleeting. Companies buy and sell domain names. Web hosting companies are bought by other companies. URLs that use to point to safe content can now point to different content. Filtering products need to be constantly updated or they lose their effectiveness. Nothing can replace proper training and adult supervision.

Here are some of the methods that are used to restrict access to web files.

• Restrict web access by file types.

  • Don't allow viewing of graphics, sound or movie files.
  • Browsers can be set not to display these type of files.
  • Some browsers don't allow the viewing of these file types.
  (End of file types)
   

• Restrict web access based on words found on the page.

  • If restricted words are found on the page, access to the page will be blocked.
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  • A problem with this method is the word patterns used to block questionable sites also ends up blocking sites that probably shouldn't be blocked.
  (End of web access based on words)
   

• Restrict access to web sites by blocking IP addresses.

  • Questionable URLs (IP addresses) are added to a list or database. The blocking can be set to deny access or only allow access if the URL is in the database or list.
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  • Rating services and some blocking software use this method. Some blocking software companies offer updates to their list of questionable sites for a yearly renewal fee.
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  • The problem with this type of blocking is that a third party decides what should or should not be filtered. Many of these companies do not fully share their blocking criteria.
  (End of blocking IP address)
   

• Restrict access to web pages by using a rating system.

  • Rating systems provide a method of assigning values to web page content. The system would allow the content to be rated suitable or unsuitable for children. Some common rating systems are RSACi, ICRA, Weburbia, and SafeSurf.
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  • These rating systems depend on webmasters embedding certain meta tags in their web pages. This way the content is rated by the content creator. The process is usually handled by the webmaster answering questions on a web page and the rating system site emails the appropriate meta tags to the webmaster who inserts the meta tags into their web pages.
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  • The biggest drawback to this system is the number of sites that have voluntarily rated their web pages. Although these rated sites number in the hundreds of thousands, there are millions of web sites that have not adopted any self-rating system.
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  • Many educational institutes have thousands of web pages they would have to rate. The labor costs associated with applying a rating to each web page makes it a huge investment of educational resources. 
  (End of rating systems)
   

• Restrict access by using a PICSRules file.

  • A PICSRules file is a text file that uses PICS rules to define what sites can be viewed by a browser. ICRA provides a free template for building your own filter. PICSRules files have an extension of .prf (profile).
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  • The downside of this method is as the file grows larger it takes more time to look up addresses and slows down the web responses. It is not that easy for novices to figure out how to allow or block sites.
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• Restrict access by redirecting requests to a local hosts file.

  • A hosts file resides on many computer platforms (Mac, Windows, Linux) and can be used by the computer to resolve a web address. A web address like www.yahoo.com needs to be resolved to its IP number (66.218.71.84). If the IP number is found in your hosts file, your computer stops looking and goes to the site listed in your hosts file. If it isn't in the hosts file, a DNS (domain name server) computer is queried and your request is sent to that IP address.
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  • Since the hosts file is checked first it provides a method that can be used to block sites that have objectionable content, are used for advertisements, or any other site that you choose to block.
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  • A drawback is if the URL is already an IP number the hosts file is not queried and the URL can't be blocked by the hosts file. Like the PICSRules file, as the hosts file gets larger web response slows down. 
  (End of hosts file)

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