CiviCRM flood control code

/**
 * Implmentation of hook_civicrm_postProcess
 * Inserting form submission time into the cache table for flood control checking
 *
 */
function yourmodule_civicrm_postProcess($formName, &$form) {
    if($formName == 'CRM_Contribute_Form_Contribution_Main') {
        $id = $form->getVar('_id');
        // note the ip could be a proxy server ip
        $ip = ip_address();
        $data = array(
            'id' => $id,
            'ip' => $ip,
            'timestamp' => time(),
        );

        $query = "INSERT INTO civicrm_cache
        (`group_name`, `path`, `data`, `created_date`)
        VALUES (%1, %2, %3, %4)";

        $params = array(
            1 => array('contribution flood control', 'String'),
            2 => array('CRM_Contribute_Form_Contribution_Main_' . session_id(), 'String'),
            3 => array(serialize($data), 'String'),
            4 => array(date('Y-m-d H:i:s'), 'String'),
        );

         CRM_Core_DAO::executeQuery($query, $params);
    }
}

/**
 * Implmentation of hook_civicrm_validate
 * Checking timestamp of previous submission time given the ip address
 *
 */
function yourmodule_civicrm_validate($formName, &$fields, &$files, &$form) {
    $errors = array();

    // verify that the last submission recorded is the same contribution page id
    // we are only going to check the date range within the same day?
    if($formName == 'CRM_Contribute_Form_Contribution_Main') {
        $id = $form->getVar('_id');
        $ip = ip_address();
        // get the last time a user has submitted the form
        $query = sprintf("SELECT data FROM civicrm_cache WHERE `data` LIKE '%%%s%%' AND group_name = 'contribution flood control' ORDER BY created_date DESC LIMIT 0, 1", $ip);

        $data = CRM_Core_DAO::singleValueQuery($query);
        $data = unserialize($data);
        if($data && !empty($data)) {
            if($id == $data['id']) {
                // check flooding interval
                $interval = time() - $data['timestamp'];
                if($interval < 60) {
                    $errors['qfKey'] = 'Maximum attempt reached, please try again later';
                }
            }
        }
    }

    return (empty($errors)) ? TRUE : $errors;
}