private static function get_enabled() {
        global $CFG;

        $active = array();
        if (empty($CFG->antiviruses)) {
            return $active;
        }

        foreach (explode(',', $CFG->antiviruses) as $e) {
            if ($antivirus = self::get_antivirus($e)) {
                if ($antivirus->is_configured()) {
                    $active[$e] = $antivirus;
                }
            }
        }
        return $active;
    }