Can someone explain this?

[Hairboi]

I just got handed down a laptop which is able to connect via the wireless to the internet. I managed to connect to (which I thought at the time) the house's router. I was happily using the internet for a few days, then all of a sudden, the mouse cursor starts moving itself, closing down windows etc. I got freaked out and shut the laptop down and plugged it into the router directly instead. I then noticed we have a Netgear router and not a Belkin one that I was connecting to.....

Is it possible that I was using someones internet and they hacked my system or something??

 

[jonifen]

As yours is a Netgear and you were connected to a Belkin, then you were definitely connected to someone else's internet

For someone to move your mouse pointer and close windows, chances are your laptop has a trojan installed (or even something innocent like a VNC server) which is allowing them to do this. Depending how their network was configured, it's unlikely to be someone from outside of it (because of routers providing NAT and not forwarding ports by default).

I'd do an antivirus scan and remember that you own a Netgear in future