This question already has an answer here:
I read in another post that wired traffic is not protected:
The only real additional threat that a malicious network administrator would pose, is that they have access to the wired side of the network also. On the wire, traffic is not protected by the same encryption (WEP/WPA/WPA2) that applies to the wireless connection. Anyone on the wire could then sniff your traffic as if it had been sent across an open (unprotected) network on the air.
If this is true, how would I know if someone is "on the wire?" I am referring to my laptop being plugged into my cable modem via ethernet cable and my apartment being a massive hotspot of wifi and ethernet. Can someone still snoop my connection if they are not physically connected to my modem?