It is increasingly common for vandals to place hyperlinks on
wiki pages to commercial sites, presumably to increase their 
{link: http://www.google.com/technology/ page rank}.
The site administrator then has to go in and clean up the mess.  Lately,
this has been happening on the http://www.sqlite.org/ site several times
per day.

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
   {link: http://en.wikipedia.org/wiki/Captcha 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.

*: Log changes by IP address and blacklist spammers.

*: If it is only possible answer 'unknown username' for spam emails. It's one
   of many part solutions. Other is to rotate domain name.