Blocks the current user's IP address.
function system_block_ip_action() {
$ip = ip_address();
db_merge('blocked_ips')
->key(array(
'ip' => $ip,
))
->fields(array(
'ip' => $ip,
))
->execute();
watchdog('action', 'Banned IP address %ip', array(
'%ip' => $ip,
));
}