So what stops outbound connections, xp sp2’s firewall only stops inbound connections (not outbound), most hardware firewalls, again only stop inbound connections (there are some exceptions).

In this case a software firewall is hardly useless, as it would appear to be the only thing that would cover outbound traffic.

So it would not be reasonable to assume if you block inbound traffic you won’t have outbound traffic. Nothing is 100% so it may be possible to get in, what’s stopping it calling home ???