[zedwill]

You can also install a honeypot. Some text links that your human visitors don't see but that bots do, and that way trap malicious bots which do not respect your robots.txt file.

There is an outgoing project: Project HoneyPot, which uses honeypots installed among their members to detect bots to build a database of malicious bots which can be consulted by their API or their plugins. They even report if there is evidence of Spam being sent as a consucuence of the bot visit.

They have plugins for wordpress among others.

http://www.projecthoneypot.org

[kakooljay]

Are honeypot strategies still effective? They talk about using hidden form fields here: http://www.rustylime.com/show_article.php?id=676

...but they add a disclaimer: "We are no longer using this method as it, after more than a year of successful use, seems to be beaten regularly now."