This free WordPress Plugin replaces user names in author pages URLs with 16 digits coded strings to enhance security
WordPress automatically creates a page for each author. There is a serious security flaw with the URLs generated from WordPress for these author archive pages. The login names from all your users are publicly visible in this URLs.
The plugin automatically replaces user names with 16 digits coded strings. The codes are generated automatically and its impossible to make conclusions about the user names. Just install and forget.