If a wifi dongle purchased in your name could deanonymize you, then why couldn't a computer purchased in your name? The MAC address of the network interface is only known to the first router of your internet connection. That is layer 2, the physical addressing layer, of the OSI model: https://en.wikipedia.org/wiki/OSI_model The internet exists at layers 3 and above. IP addresses are at layer 3, logical addressing, so IP addresses can be broadcast over the internet, but MAC addresses are not. Of course, the purpose of Tor is to mask IP addresses.