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The placing of hyperlinks in wiki like this is often called "Wiki Spam". See, for example, http://www.usemod.com/cgi-bin/mb.pl?WikiSpam, http://c2.com/cgi/wiki?WikiSpam.
So far, the vandalism seems to be confined to wiki pages. I presume that it is only a matter of time until it spreads to tickets.
Possible solutions:
- When an anonymous user enters a URL in wiki, do not make URL into a a hyperlink until it has been approved by an authenticated user. Prior to approval, the URL is shown as plain text. Authenticated users have a link after the URL which will cause the URL to be approved. Other anonymous users will see an explanation of some kind stating that the link is pending approval. This could all be easily implemented by maintaining a table in the database of approved external hyperlinks.
- Require anonymous users to log in before making changes. They can still use the user name "anonymous". The anonymous user must also supply a password which they obtain by reading a CAPTCHA on the login screen.
- A utility that allows the administrator to view all URLs in on any wiki page or ticket, and to selectively disable any that appear to be spam. This facility would allow an administrator to quickly clean up a site that had accumulated a spam load.