Phone Tracking And The Law: Clear Sailing

Written by Mark Rasch
February 21st, 2013

Attorney Mark D. Rasch is the former head of the U.S. Justice Department’s computer crime unit and today serves as Director of Cybersecurity and Privacy Consulting at CSC in Virginia.

In the ongoing Nordstrom/Euclid cell phone tracking debate, it seems that Nordstrom (NYSE:JWN) failed to ask all three necessary questions when using any technology that might raise a privacy concern. These questions are, in no particular order: Is it legal? Is it profitable? And is it wise? Ask only two of these three questions, and you can be in deep trouble.

The debate surrounds the Seattle-based retailer’s use of a vendor called Euclid, which captures information from the Wi-Fi signals of both customers and passersby.

Is it legal?
There is no specific U.S. law on whether MAC addresses are “personal information” entitled to legal protection. Moreover, U.S. law regarding things like access to cell phone records and cell phone usage probably don’t apply to the Wi-Fi portion of the device. So although it may constitute an unlawful “trap and trace” or “pen register” to capture a cell phone number or IMEI of a cell phone, these laws likely don’t apply to capturing the MAC address of a Wi-Fi-enabled device. Put simply, your iPad or Wi-Fi-enabled iPod isn’t a phone, nor is the non-phone portion of your iPhone, Blackberry, Android or Windows mobile device.

So the “ping” is probably legal. Or better yet, probably not expressly prohibited under current U.S. law (lawyer tip—always equivocate. Always.).

The next question is whether a MAC address is “personal information.” Generally, a MAC address would not be considered personal information, any more than the serial number of your toaster would be personal information. It identifies a device, not a person, and it reveals no information about that device except the manufacturer and that it is a device. Big fat hairy deal, right?

But a Wi-Fi-enabled device does reveal a lot more than a toaster. And a MAC address can reveal intimate personal information, depending on how it is used and what information it is used with.

For example, Valentine’s Day was last week, and you and your girlfriend (each with a separate device) strolled into Nordstrom. The Euclid sensor picks up the unique MAC addresses and follows the two unknown devices into the store. Yours veers off to hardware (I know, Nordstrom doesn’t have hardware, but stay with me here) and hers walks to to women’s shoes. Hmm. I detect a pattern. You then meet at jewelry and stay there for about 15 minutes. You leave together. Personal information? Maybe.

A few hours later, your MAC address again pings the store. This time, it’s accompanied by an entirely different MAC address. This time, it’s your wife’s MAC address. Busted! Hard to say that the MAC address with the traffic data is not, in some way, “personal.”

Now we add the anti-theft cameras, the parking lot cameras capturing license plate information and even the registers themselves. Pretty easy to turn an anonymous MAC address into a real-life, real-time profile of a specific person. And each bit of information is perfectly legal to capture.


6 Comments | Read Phone Tracking And The Law: Clear Sailing

  1. David Sheidlower Says:

    Another great article, Mark. But I think the idea that it is not difficult to opt out of being tracked by going to a web site and typing in your MAC address is a bit of a stretch.

    I’m not sure that most users can just grab their MAC addresses off their devices. Consider how much work the credit card industry has done in the past few years to get people to notice the three digits on the back of their cards (CSV#). Teaching people to learn what a new identifier is, how to find it, and what it is used for may not be as simple as you think.

  2. Mark Rasch Says:


    I tried to opt out FROM MY iPhone. The problem was switching back and forth between the website (and the CAPTCHA) and the settings to get the MAC address. Also, there’s a difference between a Nordstrom CUSTOMER opting out, and a passer by who has no idea that the data is being captured at all. How about a giant sign, “warning — big brother is watching! To opt out, do the following…?”

  3. A Reader Says:


    Imagine that your cell phone is repeatedly playing “I’m Mark Rasch. I’m Mark Rasch.” out of its speaker, or has a projector shining “Mark Rasch” on the ceiling and floors wherever you walked. There’s no difference between this and the WiFi broadcast other than plain old eyes and ears can’t detect it. But it’s equally there.

    You’re the one who purchased and is voluntarily carrying the device that is continually spraying “I’m 12:34:56:78:90:AB” across the 2.4GHz band. You may have the device for your own convenience. It’s entirely your choice to have the device and have the WiFi radio turned on.

    If you want to “opt out”, turn off your WiFi. And your Bluetooth. And your cellphone. And remove any RFID responding devices you have from your person, including your credit and transit and door entry cards, any RFID tags sewn into your garments, and perhaps even your car keys. And if you’re going that far, you might want to wear “CV dazzle” makeup to hide from all the cameras watching virtually every public space you enter.

    Surveillance is now ubiquitous in the public square. Does it make sense to try to ignore it?

  4. Mark Rasch Says:

    I agree that surveillance is now ubiquitous in the public square. It doesn’t make sense to ignore it. It does make sense to try to balance that with rights to privacy. I transmit my MAC address in order to obtain a signal and to log on to a service. In doing so, I do not expect to create a permanant record, available to everyone at all times of my location and movements. The logic of “you are broadcasting it so it can’t be private” can apply to (and has applied to) location data as well as the contents of cordless phone conversations. IMHO, you CAN have an expectation of privacy in public spaces — its a matter of defining its parameters.

  5. Evan Schuman Says:

    And as bad as it is today, get ready for it to get a LOT worse. Here’s a wonderful piece over at about Google Glass:

  6. Marty Ramos Says:

    Doesn’t V/MC already market credit card data such that one retailer can see visits to various other retailers…


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