How to Hide the "SpiderBlocker" Admin Menu

function plt_hide_spiderblocker_menus() {
	//Hide the "Tools → SpiderBlocker" menu.
	remove_submenu_page('tools.php', 'ni_spider_block');
}

add_action('admin_menu', 'plt_hide_spiderblocker_menus', 11);

Where do I put this code?