what the hell is steam downloading?

[Bored]

steam is taking up all my bandwidth downloading something huge at sustained 5mbps, this has been going on for hours now, there's no updating or downloading games either, it's something in the background.

any idea what this is and how to fix or cancel it?

[Apostulator]

In the top left corner, click > Steam > Settings > Downloads - then un-check "Allow downloads during Gameplay."
Then, click > Steam > Settings > Interface - and un-check "Start Steam When My Computer Starts."

You may also set Download Restrictions to only certain hours.

...as to what your Steam app is downloading/updating, I do not know; did you just do a fresh install of the Steam app/client on your computer?

[Bored]

i have neither of those checked as it is, i did not do a fresh install of steam