> I get an email from Netflix each time I log in, telling me that some new computer they have never seen me log in from has recently logged in, and that changing my password might be a geed idea if I don't recognise that computer. I'm IPv6, Netflix is IPv6, their IP checking code is still a bit behind the times.
More often than not that is done via cookies or similar technology (if using a non-browser based client).
So if you login via a browser but you have cookie blockers, or regularly clean out cookies, it'll see the browser as a new "PC" because their persistent cookie is no longer there.