在多站点安装中\'wpmu_validate_user_signup\':

add_filter( \'wpmu_validate_user_signup\', \'wpse_77904_mu_no_at_in_username\' );

function wpse_77904_mu_no_at_in_username( $user )
{
    if ( FALSE !== strpos( $user[\'user_name\'], \'@\' ) )
        $user[\'errors\']->add(\'user_name\',  __( \'That username is not allowed.\' ) );

    return $user;
}

add_filter( \'validate_username\', \'wpse_77904_no_at_in_username\', 10, 2 );

function wpse_77904_no_at_in_username( $valid, $username )
{
    if ( FALSE !== strpos( $username, \'@\' ) )
        return FALSE;

    return $valid;
}