 <p>Google not only prohibits direct personally identifiable data, but it also prohibits data that can be used to indirectly personally identify people within your own system. So in other words, if that GUID is attached to a personally identifiable info within your own system, you cannot send that data to GA, because you can easily export the GA data, tie it back into your system, and attribute GA data to personally identifiable data. </p> <p>Of course, someone would have to bring it to google's attention, and someone would have to prove there is a link to said data...</p>