So I logged into my school wifi on my laptop, and I was just wondering:
Can they still track what I do even after I disconnect? I am using my own computer (not the school's,) but is it possible that they can somehow track/monitor my activity on said computer even after I go home and use my home internet?
...or is that considered spying and illegal?
Your Laptop, Your Network
No, they cannot see what you're doing on your laptop when you're on your network, because you're using your machine and accessing the internet through an ISP that's not theirs. You're right to suspect that monitoring you in this situation would be illegal.
Their Network
When you're on their network, however, the game changes. They can monitor your internet traffic. If you're browsing by way of HTTPS, they can see what domains you visit, https://www.website.com for example, but not that you ventured to https://www.website.com/questions. In this case, the /questions element would remain hidden. Assume that your activity is being monitored while you're on their network, even when you're using your own computer.
Their Machines
I know this is beyond the purview of your question, but note that they can monitor far more when you're using one of their computers. They can, for instance, install a keylogger, have a program take snapshots of the screen at random times, etc. For this case, I invite you to explore the following thread for additional information: Can my employer see what I do on the internet when I am connected to the company network?
Your school can not intercept your network traffic when you are using your internet at home. They would have to have installed a backdoor on your device to be able to do such a thing, which would be very illegal indeed.
Note that if you use a VPN connection to some internal school network they'll be able to monitor your traffic if they own the VPN server.
A lot of devices look for known networks by sending out beacons containing the network's name. If you take the laptop places it might broadcast the name of your school's network together with your MAC address. This allows people in your vicinity to track where you've been. Also, some devices auto-connect to known networks. So an attacker could set up a network with the same name, and intercept your traffic the moment your device connects to it. If you're paranoid you can remove the network from your device or configure it not to connect to known networks automatically.
Depends on their WiFi network. If they have you install an MDM profile or agent on your computer as part of the enrollment to their WiFi network (such as ClearPass, Meraki, etc), they may be able see certain information about your computer, it’s location, and/or activity after it leaves their network.
But if it’s a plain WiFi that doesn’t require anything to be installed, then the chances are pretty slim.
As for legality... it depends on the terms you agreed to when you connected to the network.
