Keyword filters block unwanted web pages on the basis of potentially fallen words found in them. However, to be sure that a page is indeed offensive, keyword filters nowadays are not designed to block sites on the basis of just about any potentially offensive word. Instead they measure the number of potentially offensive phrases and often the number of times they occur so as to allow a limited number of occurrences in pages such as those on anatomy, forms requiring gender information, crime reports, statistical reports, administrative information, art etc. The leading keyword blockers like Dansguardian which is extremely popular on Linux or SafeSquid which is popular on Linux and Windows use this method known as a weighed keyword score.
UPDATE: Dansguardian users please refer to http://www.howtoforge.com/never-forget-to-turn-dansguardian-back-on-after-a-cyberspacejaywalk instead of the present tutorial for much faster and better results.
While Dansguardian comes configured with a keyword blocker on SafeSquid you have to visit http://safesquid.cfg/config, locate the panel titled Select a Section to Configure, click the drop-down box and select Keyword filter, then hit Submit. Once in the Keyword filter section of SafeSquid, turn the Enabled radio button on and modify the default threshold value of 100 – I use a threshold of 50 – and click Submit not in the panel high up but below the textbox labeled Template. You must also have an adequate number of rules to create these scores. To know more about SafeSquid read http://www.howtoforge.com/blocking-webpages-based-on-keywords-or-phrases-with-safesquid-proxy.
Now that your know your keyword filter is probably up you will be interested in eliminating the word probably and making sure it is indeed up! Ironically, the practice when it comes to checking whether you web filter is effective is to try to access the very adult websites you desire to block and in case your keyword blocker was not properly installed, configured or launched or cannot otherwise intercept the muck you may be in for an unpleasant surprise, more so in public or in the presence of family or minors. Nevertheless you can indeed check your keyword blocker safely by using a free web application known as Block That which is currently running version 2 full release. Enter the URL http://www.yourfilter.org in your browser’s address bar or click the link. The default action on the landing site of Block That v2 is the check which checks whether your keyword filter is working.
In the process of this check you the user or anyone looking at your monitor is not exposed to any kind of fallen content. The blue disc is the countdown timer and it counts the number of seconds left for the test to finish. Once finished the results tell you in plain English whether your keyword blocker is able to block fallen language or not. If your browser is unguarded, that is the filter is not working the test region displays an OFF sign and the result panel explains in detail the status of your browser’s keyword blocker if any is present.
However this test result is not enough. Whatever be the result positive or negative the interface will tell you that to be of use you must click the retest button to conduct the test a second time. It is the second test result which really counts, the first test is more likely to give correct results if you haven’t changed any settings recently and have started the browser afresh, e.g. when http://www.yourfilter.org is your homepage and you’ve just launched the browser. Even then it is good to retest and the owners of the application in their documentation urge users to always test twice. When you click the retest button, a message will ask you to first clear the browser’s cache and cookies. If you haven’t done so, you will be asked to click the cancel button to abort the retest, clear the cache and cookies, hit retest again and click the ok button to continue with the test. If your retest fails that means you are unprotected and if instead of using Block That you had attempted to visit an adult website you would have come face to face with the very content you wish to avoid. So, this is your chance to safely investigate what is wrong with your keyword blocker. To check SafeSquid settings visit http://safesquid.cfg.
One thing many web filters can’t do is to block websites if the https protocol is used as opposed to the http protocol. If you happen to be using Dansguardian on Linux, use one of the following commands according to your user privileges. If the first one doesn’t work try the second one. If that doesn’t work try the third.
service dansguardian status
sudo service dansguardian status
su -c ‘service dansguardian status’
This command will tell you whether the dansguardian service started properly. For more information on Dansguardian visit http://contentfilter.futuragts.com/wiki/doku.php?id=Main%20Index&DokuWiki=wdievqxsxe
For both Dansguardian and SafeSquid check if the proxy server’s IP address and port number are correct. For more help ask your Admin or use the link given above if you’re using Dansguardian. If you are using SafeSquid other than the HowtoForge link given earlier you can also get live help from http://www.safesquid.com by chatting with one of their extremely helpful engineers. When you’re satisfied that your keyword filter is ready for testing conduct the test again.
Now, if your keyword filter is working alright, you will see a red disc in the test applet area with the word ON written on it. To prevent a false negative just hit the retest button and the interface will guide you about emptying the cache and cookies before retesting.
If you wish to know how to empty the cache and cookies, just read on.
In Google Chrome web browser as shown below, click the wrench icon below the window’s cancel button top right. Click Tools and click Clear browsing data. Check Empty the cache and Delete cookies and other site data and click the arrow of the drop-down box labelled Clear data from this period. Select Everything and click the Clearing browsing data button.
In Mozilla Firefox as shown below, click Tools followed by Clear Recent History … Check Cookies and Cache. Up above in the Time range to clear drop-down box select Everything and hit the Clear Now button.
In Internet Explorer as shown below, click Tools followed by Internet Options and the General Tab. Locate the section titled Browsing history and click the Delete button. Check Temporary Internet files and Cookies and hit the Delete button. The next part is required to be done only once. Click the Settings button back in the Browsing history section. Click the radio button Every time I visit the webpage and hit Ok followed by Ok in the Internet Options main dialog.
Opera users on Windows click the Menu button as shown below, followed by Settings and Delete Private Data …. In the Delete Private Data dialog, check Delete temporary cookies, Delete all cookies, Delete entire cache, Clear Persistent Storage and hit the Delete button.
Opera users on Linux, click Tools followed by Delete Private Data and Detailed Options. Check Delete temporary cookies, Delete all cookies and Delete entire cache as shown below and hit the Delete button.
Apple Safari users click the menu icon below the maximize button as shown below, and click on Preferences. Then click the Advanced tab and click the Change Settings button and delete browsing history exactly as with Internet Explorer above.
Some of the above instruction for clearing cache and cookies may need modification depending on your browser version and platform. This has been indicated in case of Opera.
Finally, never run the Block That “test” in more than one window or tab at a time and do not blacklist or whitelist http://www.yourfilter.org or the pages to which the short URL redirects.
The documentation of Block That says if you make http://www.yourfilter.org your homepage you have the added advantage of having a number of web shortcuts at your fingertips. Look for any black and white striped square on the landing page of Block That straddling the heading. You can actually see them in pictures #2 through #4 above. Click on it from any browser any time, even before the test ends if you are not interested in testing repeatedly, and choose your web shortcut. If it isn’t listed just type your URL in the input box with or without the “http://” prefix. If at a point you have already tested you keyword blocker and only want to use Block That as a site that provides web shortcuts then it is okay to open Block That in multiple tabs and windows ignoring the automatic testing. Of course the test will then give unexpected results if its allowed to end but it’s the shortcuts you’re after at that precise moment. Remember Block That is a free service. The website team has been requesting users to tell other people about their work if they feel the web application can be of any benefit to society.
For more information check out the “Disclaimer” and “Doc” links at http://www.yourfilter.org.