What is a MAC address, and what does it reveal about me?

Solution 1:

From wikipedia's MAC address :

A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet hardware address (EHA), hardware address, adapter address, or physical address.

Although intended to be a permanent and globally unique identification, it is possible to change the MAC address on most of today's hardware, an action often referred to as MAC spoofing. Unlike IP address spoofing, where a sender spoofing their address in a request tricks the other party into sending the response elsewhere, in MAC address spoofing, the response is received by the spoofing party. However, MAC address spoofing is limited to the local broadcast domain.

In the IPv4 world, the MAC address of your computers is not propagated or detectable beyond your local network. This means that under normal browser operation (without plugin intervention), the MAC address of any computer positioned behind the router is not sent beyond the router, and so cannot be used to track you over the Internet. However, the router uses it internally in order to identify the local computers.

In IPv6, the 64 bit "host" part of the full 128 bit address is often automatically generated from the MAC address, and hence often is visible to the server one connects to. This means that outsiders may trace the MAC address of your router and your Internet-connected computers. IPv6 gives a public, routable address to every last PC, server, printer or network device (unless the router does NAT processing, which is rare in IPv6).

If Private IPv6 addresses (defined in RFC 4941) is turned on, the exposed identifier is generated as a random number rather than from the MAC. This is the default on many operating systems, but can be turned on and off. For further info see How to avoid exposing my MAC address when using IPv6.

In any case, your ISP always knows who you are and can trace anything you do, unless the traffic is encrypted by using a VPN.

Solution 2:

MAC addresses are written in the form AA-BB-CC-DD-DD-FF. The first 3 numbers (i.e. AA-BB-CC) identify a manufacturer, e.g.:

00-26-6C-xx-xx-xx   Inventec
B4-82-FE-xx-xx-xx   Askey Computer Corp

On the other hand, each MAC address is unique to every network card on earth. So it is a number uniquely assigned to you.

But nobody can link a MAC address to you.

Solution 3:

Every network interface card (NIC) is assigned from the factory a media access control address, or MAC address. In most cases, the MAC address on a network card does not change, so essentially the address identifies the physical piece of hardware. MAC addresses are necessary for routing data across networks. They don't contain user-identifiable information, and usually they aren't even visible outside of your local network.

Looking at the data you've posted, your computer appears to have two network interfaces defined, probably a wired Ethernet port and a wi-fi connection. Only one of those interfaces (with address B4-82-FE-06-96-C0) has an active network attached to it. The "/DEVICE/TCPIP..." bit is just how Windows keeps track of your network interfaces.

There is a comprehensive description of MAC addresses on Wikipedia.