WordPress Plugin default option

$default_data = Array(
    "plugin551-setting-group"   => Array(
        'checkboxoption1'       =>  'true',
        'checkboxoption2'       =>  'true'
    )
);

if ( is_admin() && isset($_GET['activate'] ) && $pagenow == 'plugins.php' ){
    global $default_data;
    plugin551_save_settings($default_data);
}

function plugin551_save_settings ( $data ) {    
    if( isset( $data['plugin551-setting-group'] )){
        array_walk_recursive( $data['plugin551-setting-group'] , 'plugin551_clean_options');
        update_option( 'plugin551-setting-group' ,  $data['plugin551-setting-group']   );
    }
}

function plugin551_clean_options(&$value) {
  $value = htmlspecialchars(stripslashes($value));
}