A MAC (Media Access Control) address is a unique ID assigned to every internet-connected machine that allows it to be identified when connected to a specific network.
MAC addresses are useful for network diagnosis because under normal circumstances they don't change, as opposed to a dynamic IP address, which can change from time to time. For a network administrator, that makes a MAC address a more reliable way to identify senders and receivers of data on the network.
Vilfo has an option MAC vendor lookup located in the General settings page, and it is enabled by default. This is done in order for users to be able to identify their devices easier.
It is possible to opt out from MAC lookup.