I happened to notice a unusual thing today when sending a friend a link to a particular podcast: the url had a unique identifying key on it. What does this mean? What can this be used for? Should people be concerned? I did some research and applied some logic and came up with the following answers.
I'd love to open a discussion on these answers. If you feel I've got it wrong, or I'm missing something, please chime in.
Are podcasters tracking me?
The answer is: some are, yes.
Should you be concerned?
No. In this case, 'you' to the podcaster is nothing more than a key number. Unless you specifically registered or pay for a podcast in some way (in other words, if you simply subscribe to any of the vast majority of free podcasts out there), your key is nothing more than a number. The podcaster cannot turn a key into "John Doe who lives at 123 Main St." The information gathered is harmless and helps podcasters get more accurate usage information.
How can I tell if I'm being tracked?
Look at the URL for the podcast. In iTunes, click the circle-I icon to the right of the name of the podcast (not the podcast download itself, the podcast channel name. If the podcast URL contains a long identifying key, chances are this key is unique to you and lets the podcaster aggregate your download information. For instance, if you subscribed to APM's Future Tense directly via the APM Future Tense web site (not by NPR's Future Tense page), you will see a URL like:
Everything after the 'uid' key is a unique identifier.
What can be done with this information?
Frankly, not much. It can help a podcaster weed out data regarding redundant downloads by the same person.
What cannot be done with this information?
This is by its very nature a DOWNSTREAM process, meaning information is sent only one way from the podcaster to your computer. No information goes the other way. For it to do so would be a function built directly into iTunes or your podcast software. It's not to say that such upstream data transfer and usage tracking isn't possible, it's just that it would be a big deal, and you would undoubtedly have heard about it if this feature was available to podcasters. Since there is, as of yet, no way to get usage data, no podcaster can gather information such as if you skip the ads or listen to a particular segment.
Why would a podcaster do this?
Getting accurate usage data is all but impossible at this time. A single person can--and often does--subscribe to the same podcast through multiple tools, especially if they are new to podcasting or have multiple computers. This can seriously skew your usage numbers. For instance, I believe Leo Laporte said in his last TWiT that they had something like 250,000 downloads. (First, wow. Second...) This does not mean that he has 250,000 users, necessarily, just that the program was downloaded 250,000 times. Being able to track users more accurately is a bedrock of any advertising model for podcasting if one is to emerge.
Is this a threat to my privacy?
No, not really. Tracking and aggregating generic usage data is harmless to you. Without an overt registration process on your part to subscribe to a particular podcast, your download of a specific podcast could not be linked specifically to you, personally. I could be wrong, but to my knowledge, spyware can't exist in podcasting since there isn't really a capacity to facilitate spyware as there is with browsers. While it is theoretically possible to track highly specific usage data and link it to you, personally, in your podcast aggregator (e.g. iTunes), these programs are, for the most part, closed systems and work a very specific way. So as long as you are using a popular aggregator, and as long as you aren't reading privacy alert headlines about iTunes doing this sort of thing, I can say with certainty that you are safe.
What can I do about this?
Simply remove the key and corresponding data from the URL. It should work just fine. Again using the Future Tense example, what was...
Note that this latter link is the one available through the NPR site. In my research, I found no identifying keys on any NPR podcast offered directly from the NPR.org site.