Something is eating up my bandwidth...... Pls help urgent?

[ChOcoLaTe HoUse®]

Whenever I connect to Internet, something starts downloading automatically, without my consent. I can see this download activity in my Bandwidth Meter.
Because of this.... my browsing speed has miserably reduced. I cant open facebook, yahoo or anything.

Plss help..... this is my new laptop which is set to automatic Windows update..... but there's no way to confirm that my Windows update is the culprit. I dont know which app or anything else is using Internet.
Plss help. I want everything back in my control. So that nothing gets downloaded or uploaded without my permission.

(i have Windows8 64bit on Lenovo G500s)
@Bob: Thanks, i did exactly what u said.... & i found something named as "fshoster32.exe" which is consuming most of the bandwidth. I googled abt it & found that it is related to F-Secure antivirus.

I forgot to mention that, I've F-Secure Internet Security 2014 installed on my computer.... but i'm still concerned whether "fshoster32.exe" is just a regular Antivirus update... or something else.