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Peter Thoeny
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Wiki Spam on Public Wikis

Wiki spam is a growing problem on public wiki sites. Actually, it is not isolated to wikis; any website that can be updated by users is a potential target for spam, such as blogs and bulletin boards. What is considered spam on a website? In the broadest sense any content that is off-topic and considered unwanted by its website users. The most common spam on writable websites is link spam: Spammers add links to their websites in many wikis, blogs, and bulletin boards, with the hope that search engines will raise the ranking of their page. In other words, spam is added not for human consumption, but for search engine spiders. This strategy works unfortunately, spam sites are listed in the first page of a search results as can be seen in this Google search for Alprazolam. You understand why if you search for Alprazolam and wiki.

What can you do as an administrator of a public wiki site?

  • Rule number one: Enable spam protection.
  • Rule number two: Remove spam as quickly as possible when it happens.
    Reason: Spammers identify easy targets by searching sites for known spam keywords. It pays off to spam sites where spam survives long enough for search engines to spider the content.

Most of the wiki spam happens on wiki pages. Anonymous users or newly registered users add link spam to their wiki homepage and other wiki pages. Spammers are getting more sophisticated. A new type of spam has emerged recently: HTML attachment spam on wikis where users can attach HTML files to a wiki. This spam is nasty because it might identify wiki sites as spam sites. It works like this: A spammer attaches a web page to a wiki with lots of ads for what they sell. Then they add link spam to many wikis, blogs and bulletin boards to raise the page ranking of the HTML page attached to the wiki.

Public TWiki sites are spam targets for some time already; it is discussed on TWiki has a BlackListPlugin that is quite effective in fighting spam. The Plugin gets updated every time a new spam twist is discovered, such as an HTML redirect obfuscated in a JavaScript eval statement. The BlackListPlugin fights spam on several fronts:

  • Multiple registrations by the same IP address in rapid succession
  • Multiple page saves by the same IP address in rapid succession
  • Saving text with known wiki-spam (spam list is maintained and shared by TWiki, MoinMoin and Mediawiki sites)
  • Attaching files with known wiki-spam
  • Attaching files with JavaScript eval statements
  • Manually maintained BLACKLIST of malicious IP addresses
  • Automatically updated BANLIST of IP addresses with suspicious activities
  • Registration form with magic number in hidden form field to make scripted registrations harder
  • Add a rel="nofollow" parameter to external URLs to defeat the purpose of spamming TWiki sites

I strongly recommend owners of public TWikis to install the latest BlackListPlugin. The reality however is that there are still many public TWiki sites that do not even have this Plugin installed. To address the issue, the TWiki team sent out several spam related alerts to the twiki-announce mailing list, and I sent personal e-mails to some site owners not on the list. Still, the awareness of wiki spam needs to be raised so that more site owners take actions.

Related links on wiki spam:

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