PHP Fatal error: Call to undefined function arg() in /var/www/drupal/modules/spam/trackback_blackhole/trackback_blackhole.module on line 70

function trackback_blackhole_init()
{
if ((arg(0) == 'trackback')) {
exit(0);
}
}

I am not a programmer, but I guess maybe the path of "trackback" is /tracker not /trackback.