Is it possible for my Roku TV and account to be hacked if someone is using the same way Wi-Fi I'm using has the password for the Wi-Fi and scan that QR code on it?
Your Roku account is online and has the standard security issues with it's own password. Your WiFi wouldn't really make a difference. I've never really used it except for testing, so I can't remember if the Roku app requires a login before it will control a Roku.
Unless the shared network isolates connected devices I'm pretty sure anyone connected to your network (Wi-Fi) can control your Roku with the app and cast videos to it. Technically they could make purchases on your Roku account by blindly sending remote control buttons, but it wouldn't be easy. I would strongly suggest adding a PIN to your account - https://my.roku.com/account/pin . You should probably look into some kind of wireless bridge that connects to your shared Wi-Fi and then allows you to connect your Roku to the bridge isolating it from the shared network. However, that kind of thing can often be troublesome to get working properly with Rokus.
If I didn't trust someone on my WiFi, I wouldn't let them on my WiFi. But I have no problem telling someone that I don't trust them.
Alternately, many network setups allow for the creation of a guest network. You could go that route, if your wireless router has the feature. If you didn't want to make it obvious, change your network SSID and password, then when you set up the guest network, use the old SSID and password for it. Your untrustworthy guest still connects as if nothing changed. Don't forget to put your stuff on the new network name.
DBDukes
Roku Community Streaming Expert
Note: I am not a Roku employee.
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My landlord rents two different apartments and provides internet service to both from the router placed in the largest apartment. The tennant in that apartment constantly logs into my Roku and manipulates the channels and the streaming services selection, turns off whatever program I'm watching in real time, whenever not turning off the router altogether in order to prevent my access to the internet entirely. This happens daily.
It's been my experience that if you have shared Wi-Fi, the other parties can hack your Roku.
The landlord should use a router that supports VLANs. They could set up isolated networks that otherwise share the internet connection.
Thanks for that little tidbit of valuable information: I'm liking the very idea of that already!
@Seensome, if your landlord won't oblige you could also look into a wireless bridge that connects to the shared Wi-Fi and then you connect your devices to the bridge. Your obnoxious neighbor wouldn't be able to access your devices, but bridges can be finicky.
Thank you @renojim. It's always best to have options. And in this case it may be best to use an option that let's me be in control of the signal.