Spambots

With most well maintained low-edit wikis if you look at Special:RecentChanges they list a sequence of: caused by spambots adding crud to the wiki. A fake user identity is registered, this one-time identity adds an external link buried in some text on the user talk page, the admin deletes the crud and blocks that identity. This still leaves the user list messy with many blocked fake users, more than real users. If the wiki isn't well maintained it will be overwhelmed with spam links.
 * (Deletion log)‎ ..
 * (Block log)‎ ..
 * (User creation log) ..

This ought to be a recognised MediaWiki bug.