Spambot prevention snippets using .htaccess and PHP

.htaccess

SetEnvIfNoCase Referer semalt.com spambot=yes
SetEnvIfNoCase Referer econom.com spambot=yes
SetEnvIfNoCase Referer buttons-for-website.com spambot=yes
SetEnvIfNoCase Referer ilovevitaly.com spambot=yes
SetEnvIfNoCase Referer ilovevitaly.ru spambot=yes
SetEnvIfNoCase Referer darodar.com spambot=yes
SetEnvIfNoCase Referer 7makemoneyonline.com spambot=yes
SetEnvIfNoCase Referer myftpupload.com spambot=yes
SetEnvIfNoCase Referer priceg.com spambot=yes
Order allow,deny
Allow from all
Deny from env=spambot

spambot_prevention.php

add_action('init', 'nebula_spambot_prevention');
function nebula_spambot_prevention(){
	//List of known spambots. The dots allow for any TLD to trigger with fewer false-positives.
	$known_spambots = array('semalt.', 'ilovevitaly.', 'darodar.', 'econom.', 'makemoneyonline.', 'buttons-for-website.', 'myftpupload.', 'co.lumb', 'iskalko.', 'o-o-8-o-o.', 'o-o-6-o-o.', 'cenoval.', 'priceg.', 'cenokos.', 'seoexperimenty.', 'gobongo.', 'vodkoved.', 'adcash.', 'websocial.', 'cityadspix.', 'luxup.', 'ykecwqlixx.', 'superiends.', 'slftsdybbg.', 'edakgfvwql.', 'socialseet.', 'screentoolkit.', 'savetubevideo.');
	
	if ( isset($_SERVER['HTTP_REFERER']) && contains(strtolower($_SERVER['HTTP_REFERER']), $known_spambots) ) {
		header('HTTP/1.1 403 Forbidden');
		die;
	}

	if ( isset($_SERVER['REMOTE_HOST']) && contains(strtolower($_SERVER['REMOTE_HOST']), $known_spambots) ) {
		header('HTTP/1.1 403 Forbidden');
		die;
	}
}

function contains($str, array $arr) {
    foreach( $arr as $a ) {
        if ( stripos($str, $a) !== false ) {
        	return true;
        }
    }
    return false;
}