How can Google spy on my local OS through a tab on a web browser?

Here's the setup: I'm running a laptop with Windows 7 Ultimate 64-bit. I have some software development skills and last week, I wrote a program (which compiles into an EXE) that launches some scripts. The scripts are very math-intensive and take hours to finish. So I let it run at night when I'm asleep. Not sure if it matters, but I programmatically added a slight "mouse jiggle" every few minutes. I move the mouse a few pixels every few minutes …

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