Wikkawiki is an engine written in PHP, which uses MySQL? to store pages. This seems to be the primary fork from the old Wakka engine.
See WikkaWiki:WikkaSpamFighting
Wikka version 1.1.6.0 has built in robot meta tags (see NoIndexHistory), also the 'SandBox' page is never indexed. We recommend you upgrade to this version, or make the change yourself (see "Resolved Suggestions" section at the bottom of WikkaSpamFighting page)
Also see the section "Spam Block for Saving pages". This seems to be the only ContentBanning patch developed so far. We recommend you use this to block repeat spam attacks linking to the same domain name. This is not a built in feature, you will need to make the code change yourself. It's a change to edit.php, addcomment.php, and config.php. This allows you to specify a single perl regular expression (example provided).
This patch would be better if it read in a separate file containing many regular expressions, one on each line. This is something of a standard which many wiki engines already follow, so by supporting this, wikka wiki administrators would be able to share blacklists, or import the blacklist which we maintain here at chongqed.org. Listing bad content within a single regular expression will mean the blacklist is less readable, and perhaps will hit size-of-expression limitations (?). So the separate file approach is something we would like to see wikka developers creating, and also including in the 'core' wikka software.
The section "Adding Random Tokens for Form Submissions" is also a good change to make. We've not yet identified this trick as one of our AntiSpamRecommendations, but it seems like something which could repel the more simplistic automated spam attacks (the majority), and there seems to be no disadvantages. Try it out, and let us (and the wikka community) know how it goes!
See also AntiSpamRecommendations