Nick Momrik

When writing comments, a lot of people type in google.com, yahoo.com, hotmail.com, and various other web sites which don’t belong to them. This plugin strips out the comment author URL whenever it contains anything from a set of words that you specify in the Options screen. The URL will never make it to the database.

Comment Author URL Stripper

Removes the comment author URL if it contains any of the specified words.

wpyb

To prevent that usernames are publically visible, the username in the author’s permalink is replaced with the author’s ID. 
In case the page is invoked with the default permalink structure, it is displayed “Page not found”.
Additionally it is possible to modify the author base. It is recommended to make use of this plugin to change it, but it also works with other plugins that have the functionality to customize the author base.

Change Author Link Structure

To prevent that usernames are publically visible, the username in the author's permalink is replaced with the author's ID.

Comment Author URL Stripper vs Change Author Link Structure