CodeIgniter Session spammed by bots

mwhitney, thank u. I use this construction, work it.
but I edit this array list
maybe somebody need this.

PHP Code:

$robots = array(
'googlebot' => 'Googlebot',
'yandex' => 'YandexBot',
'msnbot' => 'MSNBot',
'yahoo' => 'Yahoo',
'baiduspider' => 'Baiduspider',
'bingbot' => 'Bing',
'slurp' => 'Inktomi Slurp',
'ask jeeves' => 'Ask Jeeves',
'fastcrawler' => 'FastCrawler',
'infoseek' => 'InfoSeek Robot 1.0',
'lycos' => 'Lycos',
'mediapartners-google' => 'MediaPartners Google',
'CRAZYWEBCRAWLER' => 'Crazy Webcrawler',
'adsbot-google' => 'AdsBot Google',
'feedfetcher-google' => 'Feedfetcher Google',
'curious george' => 'Curious George',
'sputnikbot' => 'Sputnik',
'sosospider' => 'Soso'
);