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Logged into same network of residence, owner knows my Mac address.. what can they see?

They are techy and know my Mac address for my phone and PC.
Can they see text message to and from me? My email? My pictures and documents?... Maybe even this right now..?

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  • Knowing the MAC address is not enough to do anything. If you are using the same wifi network as they are, or if they are in control over the wifi network, then they might be able to see what you send if you are not using HTTPS
    – schroeder
    Nov 14, 2018 at 8:07
  • Not too much, in ordinary user environment you don't need to worry.
    – peterh
    Nov 14, 2018 at 9:02
  • Who controls the infrastructure? If it's them, knowing your MAC address is completely unnecessary, because they can get the data streams directly. But a MAC address is essentially equivalent to a normal house address, and you're worried about your mail. Some types of traffic (FTP, HTTP) are the equivalent of sending post cards - the contents are visible to anybody who looks at them. Some are encrypted - HTTPS, used for most websites now - is the equivalent to sending a safe. Reading cell traffic requires non-standard equipment. Nov 14, 2018 at 18:21

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I would argue that this depends on the network topology.

In a switched network, where every device is attached to a port on a switch via lan cable, the switch transports the ethernet frames only to the destination port. every other port with an attached device can not see the frames. So in a (not compromised!) switched network, nobody can read your data except the receiver.

However if every device resides in the same collision domain, for example a wifi network, then technically every device can read every frame beeing sent. Ordinary network cards refuse frames which are not adressed to their mac-address, but some network cards can be configured to listen to everything (this is called promiscuous mode). A hacker usually uses such a network card.

So, when a hacker can read your frames, the question is whats the content inside the frames. Unencrypted traffic such as http, ftp, ... can be read without a problem. So, as the other comments say, check if all your traffic uses encrypted protocols like https.

BUT to be clear, attacking a wifi network (especially when you already have access to it) isn't a big thing and there is a wide range of attacks for this exact scenario. So I would say, in a wifi network which is not controlled by your or where you don't know every member of the network, you are never 100% safe. However using https is the most important thing you can do to keep your content private.

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  • Thank you for taking the time to respond. I am not that technical. So does this mean that my text messages and Google photos can be viewed by the owner of the house? I do know the network has one IP address for all devices connected to the WiFi, i.e. printer etc.
    – Jina
    Nov 14, 2018 at 16:02
  • So it's not easy to answer your question, especially with a simple "yes" or "no". Most of the internet servces like google, whatsapp, facebook etc. use only encrypted transport with https. When visiting google.com or every other https-website, you create an encrypted tunnel between your device and the destination server which can't be viewed by any other person. However, when someone is able to compromise your network, he can act as a man in the middle and sniff your data. But that takes time, effort and knowledge.
    – Alex
    Nov 15, 2018 at 7:17
  • In addition, modern browsers and apps may notice that somethings wrong (faked TLS-certicicates etc.) and inform you about that. Either they ask, f you really want to continue, or they prevent you from using this untrusted connection. So all in all I would say, alltough you are never 100% safe in an untrusted network / wifi, it's not that easy for the average John Doe to read your chats or view your images. It takes knowledge and effort. So don't panic but act responsible and thoughtful with your data.
    – Alex
    Nov 15, 2018 at 7:25
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They can set up a packet sniffing program such as Wireshark to intercept all communications. As long as the websites you visit have an https - you're protected. As for apps and other things, try to find out if they use TLS encryption. Even with encryption/https they can see what IP addresses you connect to. If you don't set up your own DNS settings (with DNS encryption) they can see what domains you access. So if you type in google.com they can see your device made a DNS request for that but that's it they cannot see what you do on Google.

Perhaps you may be interested in using a VPN

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