check scheduled events such as the search for updatings, some programs put them at 3-5 nights
^ This is the most likely cause. Hijackers do exist of course, but I've never heard of anyone who had a real life "Omg somebody else is controlling my pc from afar" Hollywood-esque scenario. I used to joke that my laptop was haunted since it would boot up in the early am hours while I was asleep relatively often, however I forgot that I was merely putting it to sleep all the time and not shutting it down completely. Turned out that I had a program that regularly updated at 3am. Also, if you ever have those "You must restart your computer to completely finish installing windows updates" pop-ups that start a 15 minute countdown until your system restarts, and you click "remind me in 4 hours" and then forget about it... well, if you put your pc to sleep, 4 hours can pass and then your pc seemingly "wakes up on its own."
Also, to avoid sharing things on torrent programs, I always uninstall bittorrent after I use it to download something, otherwise it is almost always running in the background and sucking up my internet speed/connecting to who-knows-what across the internet. I've got the installer downloaded and saved to my pc, so whenever I want to get another torrent re-installing the program takes me no more than 20 seconds.
