This plugin will allow you to remove an unwanted author-URI entered by a commenter with one single click of your mouse.
Download the archive and extract the two contained files:
Upload the files to the plugin-directory of your blog. This should be
After that, both files should be located at that directory. Do not create a subdirectory to store the files there!
Now, go to the plugins-section of your dashboard, look for the entry called Comment URL Control and press activate.