Nofollow Comment Author Links

<?php
add_filter( 'get_comment_author_link', 'scseed_nofollow_comment_author_links' );
if ( ! function_exists( 'scseed_nofollow_comment_author_links' ) ) {
    function scseed_nofollow_comment_author_links( $link ) {
        if ( strpos( $link, '<a ' ) === false ) {
            return $link;
        }
        // Replace or add the rel attribute with nofollow + ugc.
        if ( preg_match( '/\srel=["'][^"']*["']/', $link ) ) {
            $link = preg_replace( '/\srel=["'][^"']*["']/', ' rel="nofollow ugc"', $link );
        } else {
            $link = str_replace( '<a ', '<a rel="nofollow ugc" ', $link );
        }
        return $link;
    }
}