It's theoretically possible, but practically difficult. They can tell whether you loaded something from fast.com or netflix.com prior to the data stream, or th

It's theoretically possible, but practically difficult. They can tell whether you loaded something from fast.com or netflix.com prior to the data stream, or they can give full speed initially and throttle after a minute or two (longer than people's patience for a speed test, but far shorter than a movie). It's difficult because Netflix can respond to any such technique by taking steps to make it less obvious, so you just end up with one of these cat-and-mouse games.