The XWiki project offers several solutions to help fight spam. These are especially useful when XWiki is used as a public site.

CAPTCHA

You can enable Captchas both on the registration screen and for comments. 

You can also use the XWiki Catpcha module if you need a tighter integration in your own wiki pages / wiki application.

Notifications

You can choose to be informed by mail (even in real time) about changes done to your wiki, and thus be able to quickly revert spam. 

You can also install the IRC Bot Application to get instant IRC notifications when a page in the wiki is modified.

Delayed Indexing

You can implement Delayed Indexing to discourage spammers. It tells search engines to not index pages that were recently updated. On an active wiki, spam will be removed very quickly by community members. Once a page has not been edited for a while, you can assume the community approves of the pages content and thus is spam-free.

This can be achieved by editing the "HTTP META INFO" section of the "Page Element" Administration section. For example you could decide to wait 5 hours after a page has been created before allowing it to be indexed by using:

AntiSpam Application

Last but not least, you could install the AntiSpam Application which provides 2 main features:

• Ability to prevent spam from being entered (by filtering on keywords)
• UI to easily remove spam content and all content entered by some given user