Overview

LinkSpam is a common problem for wikis, as a web page that anyone can edit is a juicy target for a spammer looking to increase their search engine relevance. FlexWiki incorporates several features to increase its resilience to LinkSpam. One of these is support for CAPTCHA. Documentation for the others can be found via the WikiSpam topic.

What is CAPTCHA?

CAPTCHA stands for Completely Automated Process to Tell Computers and Humans Apart. As the name suggests, it is a method for distinguishing automatic postings (sometimes called SpamBots) from human posters. Note that CAPTCHA cannot prevent human spammers from putting LinkSpam onto a page...it can only reduce the incidence of automated spam.

You can read more about the principles behind CAPTCHA here Essentially, however, the idea is to require a task to be performed before an edit can be made. The task is designed to be something that humans can do easily, but that computers cannot.

How does CAPTCHA work in FlexWiki?

In FlexWiki, the task used to distinguish between automated posters (SpamBots) and humans is to copy a series of digits from an image that has a lot of noise in it. Computers are not very good at recognizing images in a noisy environment, whereas humans are quite good at this. When CAPTCHA is enabled (see below), the user will see an image like the following:

By entering the number from the image in the text box and then clicking "save", the edit is allowed. Otherwise, an error message is displayed and the user is asked to try again with a different number (in case the image is too difficult to read).

What versions of FlexWiki support CAPTCHA?

CAPTCHA support is present in FlexWiki 2.0.0.42 and later.

How do I configure CAPTCHA support?

CAPTCHA is enabled wiki-wide in the flexwiki.config file. There are three elements that control CAPTCHA support: <RequireCaptchaOnEdit>, <CaptchaKey>, and <CaptchaLinkThreshold>.

<CaptchaKey> is the encryption key used to encode the CAPTCHA value so it can be compared to what the user typed in. It should be set to a random, sixteen-digit hex value by the wiki site administrator.

<RequireCaptchaOnEdit> controls if and how CAPTCHA is utilized. It can be set to one of four values:

• Never (the default). CAPTCHA verification is never required.
• Always. CAPTCHA verification is required on every edit.
• IfAnonymous. CAPTCHA verification is only required if the user has not authenticated (is anonymous). Authenticated users are not required to pass a CAPTCHA test.
• WhenOverLinkThreshold. CAPTCHA verification is required when more than a certain number of http or https links (as defined by <CaptchaLinkThreshold> are added as part of an edit. Note that because FlexWiki needs to see the text before it can determine if the link threshold has been surpassed, users will need to click Save twice: after the first time they will be shown the CAPTCHA sidebar and given the opportunity to verify the CAPTCHA code.

<CaptchaLinkThreshold> is an integer that defines the smallest number of http or https links that must be added to trigger CAPTCHA verification when <RequireCaptchaOnEdit> is set to WhenOverLinkThreshold.

Examples of CAPTCHA configuration

CAPTCHA off

 <configuration>


   <!-- Other FlexWiki configuration goes here -->


   <RequireCaptchaOnEdit>Never</RequireCaptchaOnEdit>
 </configuration>

CATPCHA required on every edit

 <configuration>


   <!-- Other FlexWiki configuration goes here -->


   <!-- Set to a random, 16-digit hex value --> 
   <CaptchaKey>193113AB6576AD7C</CaptchaKey>
   <RequireCaptchaOnEdit>Always</RequireCaptchaOnEdit>
 </configuration>

CAPTCHA required only for anonymous users

 <configuration>


   <!-- Other FlexWiki configuration goes here -->


   <!-- Set to a random, 16-digit hex value --> 
   <CaptchaKey>193113AB6576AD7C</CaptchaKey>
   <RequireCaptchaOnEdit>IfAnonymous</RequireCaptchaOnEdit>
 </configuration>

CAPTCHA required only when three or more links are added as part of an edit

 <configuration>


   <!-- Other FlexWiki configuration goes here -->


   <!-- Set to a random, 16-digit hex value --> 
   <CaptchaKey>193113AB6576AD7C</CaptchaKey>
   <RequireCaptchaOnEdit>WhenOverLinkThreshold</RequireCaptchaOnEdit>
   <CaptchaLinkThreshold>3</CaptchaLinkThreshold>
 </configuration>