The interesting thing is any network service tends to open ports, and other local-only applications still tend to as well. This was de facto for windoze services for years, since they didn't have anything like unix sockets to avoid network port usage. They usually restrict port usage only to 127.0.0.1, but if ebay or any other malicious website is using their scripts against you locally, they HAVE access to even these local only ports.
Even iptables won't help you here since your pc IS the trusted source AND destination for the network traffic. No one blocks 127.0.0.1 going to 127.0.0.1, and apparently they are counting on that with this technique.
Even worse, I think about corporate environments where this can be used to scan for other more "internal" web resources in use in the enterprise.
Apparently nothing new though, found this 2 years ago for Halifax bank doing the same thing.
-mb