Version 2.4.1 of the legacy Akismet plugin is now available. The 2.4 branch of Akismet is for old versions of WordPress only, WP 2.9 and earlier.
This is a security update. 2.4.1 fixes a XSS vulnerability.
Anyone still using an old version of WordPress should update to Akismet 2.4.1:
Users of WordPress 3.0 and higher can ignore this release. Akismet 2.5.6 is the current plugin version for WordPress 3.x.
We’d like to remind all users of old versions of WordPress that the latest stable version includes many security updates and improvements to WordPress itself.