mrapi on "Visits on the site counted twice"

Hi,I found on a tutorial a code for a plugin that counts visits on the site,I put it on the server and something strange:90% of visits are counted twice.
http://img585.imageshack.us/img585/3255/kgof.jpg

On localhost tests,is seems to work fine,that is the code:

<?php
/*
Plugin Name: Count visits
Author: User
Version: 1.0
 */

function bdetector_activate()
{
	global $wpdb;

	$table_name = $wpdb->prefix . 'bdetector';

	// will return NULL if there isn't one
	if ( $wpdb->get_var('SHOW TABLES LIKE ' . $table_name) != $table_name )
	{
		$sql = 'CREATE TABLE ' . $table_name . '(
				id INTEGER(10) UNSIGNED AUTO_INCREMENT,
				hit_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
				user_agent VARCHAR (255),
				PRIMARY KEY  (id) )';

		require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
		dbDelta($sql);

		add_option('bdetector_database_version','1.0');
	}
}

register_activation_hook(__FILE__,'bdetector_activate');

function bdetector_insert_useragent()
{
	global $wpdb;

	$table_name = $wpdb->prefix . 'bdetector';

	$wpdb->insert($table_name,array('user_agent'=>$_SERVER['REMOTE_ADDR']),array('%s'));
}

add_action('wp_footer','bdetector_insert_useragent');

Thanks for any tip