Now, correct me if I'm wrong, but this doesn't, actually, do anything. As far as I knew, your MAC address was only relevant on the given network you are on. So,

Now, correct me if I'm wrong, but this doesn't, actually, do anything. As far as I knew, your MAC address was only relevant on the given network you are on. So, if you're on a Wireless network, this is useful, Google knows where that access point is, roughly. This does not, as the article seems to imply, let Google "cross reference the Mac address of a user's connection with their real identity and virtual identity". As far as I know, a website does not have the capability of pulling the Wireless MAC address from a router, through the browser. (Please note, this may be incorrect, as I am not an expert in networking, or web browsers, however, I have dabbled in both, and have at least a working knowledge of both) A MAC address is used in communication on a Network. It is a unique "code" for each network interface. In theory, it should only be available to those on your direct network. Unless there is some sort of protocol I am un-aware of, routing across networks must be done by IP address, so outside of your own network the MAC address is useless. Now, when it trying to cross reference a MAC address (tied to the hardware) with a user account, I don't see how Google could find the Wireless MAC address from one of their servers. Unless they use an exploit to run MAC address gathering code from the browser, I can't see any way for them to get that information to cross reference the user. On top of that, this would only be slightly more accurate than the exist GeoIP databases. Your wireless access point has a range of roughly 100 feet or more. A GeoIP database can be accurate to the block you live on. It seems fairly comparable.