Automatic blocking doesn't work cos they are constantly coming up with new ways to bypass blocks.

Here's what I use. There's a free tool called Windows Ultimate Tweaker. It'll help with basic settings.

Next, Du Meter - shows network traffic right on taskbar. If I'm not actively using the internet and Du Meter shows 1MB/s, I get suspicious.

Finally BWMeter. I'll say it's little snitch for Windows. It'll alert you any time an application tries to access the internet. You can allow/forbid temporarily or permanently.

They are all light on resources. BWMeter's UI isn't great but it gets the job done.