Session visible on other computers?

Session visible on other computers?

I have a strange issue, where basically i have a shopping cart using a
session. When i deploy the site using IIS7 all looks fine. I add a product
to the session on one pc and it displays in my basket. When i access the
site from another pc the basket has this item in it!!??
its my understanding that a session instance is unique per user browser is
this correct? and if so, how have i managed to do this? I know its
probably something stupid but i can't figure it out, any help is much
appreciated!
My session cart code is as follows
#region Singleton Implementation
public static readonly ShoppingCart Instance;
static ShoppingCart()
{
// If the cart is not in the session, create one and put it there
// Otherwise, get it from the session
if (HttpContext.Current.Session["sCart"] == null)
{
Instance = new ShoppingCart();
Instance.Items = new List<CartItem>();
HttpContext.Current.Session["sCart"] = Instance;
}
else
{
Instance =
(ShoppingCart)HttpContext.Current.Session["sCart"];
}
}
protected ShoppingCart() { }