Esse é um tutorial básico para criar uma classe que identifique se o acesso está sendo feito por um Bot.

<?php
class BotIdentifier {

protected $arrstrBotMatches;

function __construct() {

//array of bots/spiders
//You can add bots that are hitting your site see your apache servers log.
$arrstrBots = array (
‘googlebot’ => ‘/Googlebot/’,
‘msnbot’ => ‘/MSNBot/’,
‘slurp’ => ‘/Inktomi/’,
‘yahoo’ => ‘/Yahoo/’,
‘askjeeves’ => ‘/AskJeeves/’,
‘fastcrawler’ => ‘/FastCrawler/’,
‘infoseek’ => ‘/InfoSeek/’,
‘lycos’ => ‘/Lycos/’,
‘yandex’ => ‘/YandexBot/’,
‘geohasher’ => ‘/GeoHasher/’,
‘gigablast’ => ‘/Gigabot/’,
‘baidu’ => ‘/Baiduspider/’,
‘spinn3r’ => ‘/Spinn3r/’ //add comma seprated bots here
);

//check if bot request
if( true == isset( $_SERVER[‘HTTP_USER_AGENT’] )) {

$this->arrstrBotMatches = preg_filter( $arrstrBots, array_fill( 1, count( $arrstrBots ), ‘$0’ ), array( trim( $_SERVER[‘HTTP_USER_AGENT’] )));
}
}

function getBot() {

//check if bot request and return the identified bot.
return ( true == is_array( $this->arrstrBotMatches ) && 0 < count( $this->arrstrBotMatches )) ? $this->arrstrBotMatches[0] : ‘Not a bot request’;
}

//isBot() can be used to check if the request is bot request before incrementing the visit count.
function isBot() {
//check if bot request.
return ( true == is_array( $this->arrstrBotMatches ) && 0 < count( $this->arrstrBotMatches )) ? 1 : 0;
}
}

?>

para testar chamamos a função:

// $_SERVER[‘HTTP_USER_AGENT’] = ‘Googlebot/2.1 (+http://www.googlebot.com/bot.html)’;

$objBot = new BotIdentifier();
echo ‘<b>User Agent: </b>’ . $_SERVER[‘HTTP_USER_AGENT’];
echo ‘<br><b>Is Bot/Spider: </b>’ . $boolIsBot = $objBot->isBot();
echo ‘<br><b>Bot User Agent: </b>’ . $strBot = $objBot->getBot();

?>