Can someone please tell me or explain to me what virus infected to me or how my computer got hacked?
I came back from a 2-day vacation which at the hotel I was at, I signed into Netflix and Steam, but cleared all of the data after I got done. When I got home, I started my computer and started doing what I usually what I do on my computer time. Signed into Steam, TFoutpost, and Netflix. As I was finishing an episode of a show I was watching, a command prompt opened for a split second, all I could read was "System32." I quickly started scanning with Malwarebytes and Windows Defender, but they couldn't find anything wrong with my computer, but more command prompts were opening and things installing, so I just unplugged my computer. I turned on my other computer to check what this attack might have been, then I saw it. Another Command Prompt. I quickly yanked the power cord from the wall.
Since then my router's name and password has been changed, my second computer factory reset (haven't been used though,) my main computer being taken on the shop. Since then, my sisters and dad haven't suffered any attacks. I recently got a call from the shop that my computer was running slow and the most they could do is just reboot my computer to factory settings. I asked what was wrong with my computer or how it even happened, they said they didn't know.
And this is why I'm here, to ask questions on how to help this.
If they get my computer running again and cleaned, is there a possibility that the attacker (if it was just a hacker) could get in and just do the same thing? If it wasn't a hacker, does anyone know what it was and how to stop it from happening again? What could I do to keep my computer safe? And would it be safe to connect to the internet on my now cleaned computers to my family internet, without fear of whatever happened coming back for not only my computers, but my family's?
A fast response would be loved, but I understand if it takes time
Additional Info: Both computers were HP computers running Windows 8. The one at the hotel was running slow. I thought it was a Heartbleed bug via Netflix, but I don't think they'd be able to install things or even crash a computer.