Version 1.6.2b of WP Contact Form III is a security update, and I encourage everyone who use the plugin to upgrade.
Download WP Contact Form III 1.6.2b
The new version of the plugin requires at least WordPress 2.6, so while you’re at it you can upgrade to WP 2.6.1 as well
I really hope I’ve fixed all security issues with the plugin this time, and I have to admit that if there is any other issues, I do currently not have the knowledge to fix it. But the plugin is more secure now than what it used to be.
And a special thanks to Pascal Birchler for reporting the security problem.
Update Aug. 17: The version 1.6.2d on WordPress’ Plugin Directory is the same as this one (1.6.2b), - I messed up when updating the plugin as I’m still learning to use SubVersion.