The very popular WP Hashcash plugin for WordPress has been modified to work on the WordPress MU signup page.
WP Hashcash is an anti spam plugin that protects blogs from comment spam. It does this with Javascript and is quite successful. I worked on it over the last few days and the plugin now offers the same protection on the WordPress MU signup form!
This is the first release of the code so handle with care. Grab the latest version (version 4.2 as of this moment) from the download page. Unzip it and copy wp-hashcash.php into wp-content/mu-plugins/ and visit “Site Admin” -> “WordPress Hashcash” to confirm it’s working.
Now logout and create a new blog, just to make sure everything is working ok. Occasionally some users will have problems registering, and those that have Javascript turned off won’t be able to create a new blog at all. That’s the downside of using this plugin unfortunately.
Keep an eye on the stats counter on the admin page. I want to hear how well this works on your site!