question about cartID

[Guest]

i'm changing the checkout process on oscommerce, so we can use it on our website and i was wondering if someone could tell me what's the actual purpose of this code

 

// avoid hack attempts during the checkout procedure by checking the internal cartID

if (isset($cart->cartID) && tep_session_is_registered('cartID')) {

if ($cart->cartID != $cartID) {

tep_redirect(tep_href_link(FILENAME_CHECKOUT_SHIPPING, '', 'SSL'));

}

}

 

i know the comment say to avoid hack attempts, but can someone explain how it works. thanks.