Version 1.1 User's Guide
HostBlock: Simple, Effective Adult Content Filtering	Previous | Next Contents

The HostBlock plug-in is an alternative content filtering mechanism that can be used in conjunction with or in place of the PICS filtering plug-in. HostBlock provides an automated adult-content filtering mechanism that is substantially easier to configure than PICS and does not require external ratings services or reliance on Web developers to embed PICS ratings tags in their pages. However, HostBlock is also much less flexible and because it is an automated process, may make filtering mistakes a human reviewer would avoid.

How Host Blocking Works

The host blocking filter can be thought of as two components. First, a list of "denied hosts" is maintained. When a request is made of WebDoubler for a file on a denied host, the request is simply and immediately refused. Another list of "allowed hosts" is also kept, and requests for hosts in this list are always immediately accepted, even if they are also in the denied hosts list.

Keeping a simple list of denied hosts makes it very easy for the WebDoubler administrator to block servers that are inappropriate. Of course, not only adult Web sites can be blocked. For example, schools can choose to deny access to video game, sports, or other recreational Web sites.

The second component of HostBlock is a filter that scans HTML pages for words or phrases deemed inappropriate. When a page is found that contains one of these words or phrases, the page is immediately truncated and the host is automatically added to the denied hosts list.

Advantages And Disadvantages

Some WebDoubler administrators may choose to use content filtering as a non-critical deterrent to inappropriate Web use by their organization. For these people, the HostBlock provides an easy to use and very fast alternative that can be used with a minimum of maintenance.

Other administrators rely on content filtering as a more important component of their Web access strategy. If content filtering, particularly blocking adult content, is of primary importance in your organization, then it is crucial that you understand the advantages and disadvantages of the content filtering approach that you choose.

In general, the primary disadvantages of using an automated filter like HostBlock are:

• Incorrect denial of sites that should be considered appropriate.

• Incorrect access to sites that should be considered inappropriate.

Both of these potential problems are due to the fact that no person is looking at a given page and making a determination as to it's suitability for a certain audience. PICS, for example, solves this problem by allowing a person to review and rate content. This person is typically either the developer of the Web page in question or an independent third party.

The HostBlock plug-in minimizes the problem of denying acceptable sites by allowing you to specify a list of allowed hosts. If a Web site is ever incorrectly blocked, you simply add it to the allowed list and it will be permitted from then on. This problem can also be limited with a more restricted list of inappropriate words and phrases. In other words, if your primary concern when using HostBlock is that sites will be incorrectly blocked when they should be allowed, then you can specify a smaller list of inappropriate words and phrases to determine when a site should be blocked. The list will not only be shorter, but the words and phrases you choose will be "more aggressive", and you will not include words that could potentially be used in appropriate Web sites.

Allowing access to sites that should be denied is potentially a larger problem. The problem can be minimized by specifying a list of inappropriate words and phrases that is very restrictive. Doing this will lead to more incorrect denials, so the WebDoubler administrator should be prepared to add new sites to the allowed list more frequently.

The advantages of WebDoubler HostBlock include:

• Performance - Because the HostBlock plug-in does not need to look up ratings with a third party service, performance is excellent. In most cases, WebDoubler's overall performance will not be effected noticeably when this plug-in is used.

• Instant Updates - Using people to rate pages is often a problem for many ratings services, because potentially inappropriate sites must be identified and a person must review and rate the content. In some cases, sites may be allowed incorrectly using ratings services because the site in question simply hasn't been rated yet by the service, or the rating hasn't yet been added to the filtering database. Since HostBlock reviews sites as they are loaded, the filter is always applied immediately.

• Consistency - Ratings systems based on Web developers rating their own content is, as of this writing, not reliable. Even third party ratings services are subject to a certain amount of subjective error in developing ratings. HostBlock will always apply the same rules to every site, providing a consistent method of rating content.

• Cost - There are no monthly service charges for using HostBlock.

• Local Control - As the WebDoubler administrator, you have ultimate control over which Web sites are permitted and which are denied. Sites that may be deemed appropriate in some environments can be specifically denied in yours, and vice-versa.

Of course, you can also choose to use PICS, a third party rating service, or any other filter in conjunction with HostBlock. For example, if you are using a third party ratings service, you may install HostBlock with no inappropriate words or phrases specified at all. In this case, sites will never be automatically denied, since you will be relying on your ratings service to block inappropriate content. However, you will also be able to manually add specific Web sites that are not to be allowed at your location. These sites would then be blocked in addition to those blocked by your rating service.

Getting Started With HostBlock

To use the HostBlock plug-in, open a Web browser and access the WebDoubler Administration home page as described in the "Plug-In Administration" section of the this guide. Click the "WebDoubler HostBlock Administration" link to open the HostBlock Administration page. HostBlock can only be configured using the Web administration interface.

Figure 46: The Main HostBlock Administration Page

At the top of the page, the "Statistics" section will show you how many pages have been passed and how many have been denied since WebDoubler was last started.

Options

The first option available is "Host Blocking", which can be set to "Enabled" or "Disabled". This allows you to easily suspend blocking if you need to temporarily.

In the next field, specify the path to the page you would like returned when a page is blocked by HostBlock. You can specify any page you like, although a default is provided. To make changes to the "Blocked" page, it may be easier to simply edit the default page provided than to create a new page and change the "No Access Page" field to use it.

The HostBlock plug-in also provides the ability to log all requests that are blocked. We recommend that you enable the block log so that you can easily see which pages are being blocked and why. If a site is incorrectly blocked, the log file can help to show you what word or phrase was deemed inappropriate and caused the site to be added to the denied hosts list. The log file name and it's location (relative to the WebDoubler folder) can be set by entering the path to the log file in the "Log File Name" field.

As described above, HostBlock provides two distinct services: blocking hosts that appear in the list of inappropriate hosts, and adding hosts to this list when certain words or phrases are encountered. Scanning for these words and phrases can be disabled if you choose by setting the "Word/Phrase Scanning" option to "Disabled", so that only domains you specifically identify and place in the "blocked hosts" list will de denied. In most cases where your organization chooses to block adult content, this option should be enabled. Configuration of the word/phrase filter is described in the next section.

When you make changes to any of the settings in the "Options" section of the administration page, be sure to click the "Save Changes" button to have the settings permanently saved.

Blocked Words/Phrases

To manage the lists of words and phrases that will be used to filter content, click the "Edit Word/Phrase Lists" link on the main HostBlock administration page. Before you proceed, please note the warning that accompanies this list. Some of the words and phrases in this list are, by necessity, quite offensive. We apologize for any difficulties caused by maintaining this list in WebDoubler.

Once you open the "Edit Blocked Words/Phrases" page, you will see 3 different lists that can be maintained. The first two lists, at the top of this page in the "Blocked Words/Phrases in Web Pages" section, are used when Web pages are scanned as they are being served. Only one of these lists is ever being used at any one time. HostBlock provides two lists to allow the default configuration to be easily changed from more conservative (restrictive) to more liberal (permissive). Having two lists also allows you to better configure HostBlock for your organization, letting you test different filtering phrases and quickly determine their relative effectiveness.

To select which phrase list is to be used for filtering, simply check the radio button above the list you would like to use. By default, the "Conservative" list is used, and you will notice that this list includes all the phrases from the "Liberal" list, plus many additional phrases that make HostBlock more restrictive. As described above, the more phrases that are used to restrict access, the greater the likelihood that acceptable Web sites may occasionally be incorrectly blocked.

To add words or phrases to any of the phrase lists, simply go to the end of the list and enter the word or phrase. You can enter several phrases by typing return between the entries. When done, don't forget to click the "Save Changes" button.

The "Blocked Words/Phrases in Search Fields" operates slightly differently, and under slightly different circumstances. Instead of scanning every word of every page that is served through WebDoubler, this list will be used to scan search words sent to hosts listed in the "Allowed List". In other words, search engines like Yahoo and Alta Vista will generally be included in the "Allowed List", to ensure that access to these sites is never denied. When a user within your organization submits a search request to one of these search engines, their request will be scanned for inappropriate phrases. This is done because even allowed and otherwise acceptable sites will sometimes serve adult content when searches for adult-oriented material are sent.

This list is updated in the same way as the other two, described above. One important difference, however, is that entries in this list may include an asterisk ("*") as a wild card. This allows "porn*", for example, to match and block searches for "pornography" and "pornographic" with a single entry.

Blocked Hosts And Allowed Hosts

The word/phrase filter described above will automatically add domains deemed inappropriate to the "Denied List". As the system administrator, you can also block sites by adding domains to this list manually, or unconditionally allow sites by adding them to the "Allowed List". To add domains (either domain names or IP addresses) to either list, enter it into the appropriate "Host Name/IP Address" field and click "Block Host" or "Allow Host" as needed.

These lists can also be managed on the WebDoubler server by editing the "Allowed Hosts" and "Blocked Hosts" files directly. Both of these files are located in the "HostBlock" folder in the WebDoubler root folder. The files are very simply the list of allowed or blocked domains, separated by returns. This makes it very easy to import large lists of domains that should be denied, for example, regardless of the source of the list. In general, you should never need to remove domains from either list. If you do find that a domain must be removed, it can be done by editing the "Allowed Hosts" or "Denied Hosts" file directly using a standard text editor.

The complete lists of allowed or blocked domains can be viewed by clicking the "View Blocked Host List" or "View Allowed Host List" links.

Optimizing HostBlock

When WebDoubler is installed, HostBlock is automatically preconfigured with very effective filtering word/phrase lists and allowed host lists. However, as new Web sites come on-line, the information in these lists may become out of date or less than optimal. We encourage you, the WebDoubler administrator, to take a proactive role in managing your HostBlock filter. In addition, a Web page on the Maxum Web site is maintained that includes information on keeping HostBlock up to date and optimized. For the latest information on recommended HostBlock settings, visit:

http://www.maxum.com/WebDoubler/HostBlock.html

In addition, if you discover additional search sites that should be added to the "Allowed List", words or phrases that make HostBlock filtering more effective, or other configuration optimizations, please send them to "support@maxum.com". This will help us to keep the HostBlock Web page up to date and an effective resource for real-world situations.