Netflix is logging your whole activity. Meaning IP-address / device and the time of course. I don't know the exact data which Netflix is aquiring from your device, but it's not difficult to get your hardware ID you are using when logging in with your mobile device. So, while your IP-address is changing, your hardware ID stays the same. Thus, they are aware of you being the user of that mobile device.
My IP-address changes each 24 hours, or when I reconnect to my provider. But try to explain two or more Smart TV's which are actually stationary with each having a different IP-address streaming Netflix at the same time. All that stuff is being logged. You can also verify this on your own for the last 60 days.
Just want to point out that MAC address information is not shared over an HTTPS connection. It's possible if you download their Netflix app that they can get access to this data, but even so, that's sort of irrelevant, as that doesn't give away any information about where the device is located. Even moreso than that, Netflix is a company, they aren't a government, so they don't have ISP records to look through or anything more than you or I do.
But if you think about it logically, why would a company like Netflix go through all that trouble when the power they *do* have allows them to just ban these accounts. I would bet that they have automated alerts for when accounts get unusual activity, and the obvious solution to me would be to just ban those accounts before it got out of hand. You think they would try and identify a handful of individuals (who may not have much money anyways given their use of a stolen Netflix account) and take them to court for a negligible amount of money.
Like I said, I don't know what information / data is being send to Netflix. I can see that they know on what kind of device you are logged in. When I check my Netflix app it shows me all the hardware information of my device, like OS, Build, model and SN. This info could be send to Netflix to determine your device. That data alone doesn't give away any information where it is located which is quite obvious, but that's why you also log the IP address used with the device. Now I know what device and where. But what about the user? How does someone knows if the user is using the IP or has used in the past?
This is quite easy. Especially in the US, since private data is a myth.
So, that's how it will go:
Netflix logs the activity of their users. They plan to use a tool to track users activity. The tool finds a user which is streaming on 4 different device ( Smart TV) with each Device having a different IP address.
Netflix will now collect all the logs for a specific timeframe and verify the issue on the entire time until it gets excessive enough to warrant legal actions. That could be done by a tool automatically.
Now, how to determine the IP addresses of the users, since you said it's not a government? In germany, every lawyer is capable of asking the ISP for the private data of IP addresses during a specific time. Due to our private data policy, they have to be quick.
In the US even a detectice can get that information. So, Netflix will get a lawyer who acquires the necessary information and all of this will be used as evidence against you.
They will ban your account, but also ask you to pay for the damage done including lawyer costs and so on. Netflix gets money and laywer will also be happy with more money.
And if you saw the links I've posted they already plan on using a tool to go against account sharing. And they reason for all this? Money of course.
In germany, laywers specialized in sending thousand of warnings to people who got or didn't got caught by copyright infringment. They have to pay 800-1100€ if they don't want to get sued. As evidence they'll list ip address and time. They got your private data from the ISP.
They made a business out of it.
All I want to say is be aware of what you are doing and if the terms of agreement support it. You never know what could happen.