New User from US
joined:Feb 18, 2014
Windows 10 apparently introduces a new "Windows Update Delivery Optimization" (WUDO) that allows peer-to-peer delivery for future Windows updates. This essentially makes every Windows 10 user a peer in that network, effectively hijacking your connection to serve others updates.
While this should speed up getting updates, it uploads without your knowledge as it's not opt-in - it's enabled by default.
ComputerWorld has a decent summary
[computerworld.com], screen shot on how to turn it off and a link to the redditor who discovered it.