There's No Such Thing As An Anonymized Dataset

from the statistical-analysis dept

Slashdot reports that a pair of computer scientists have figured out how to de-anonymize the "anonymous" data set that Netflix released as part of its million-dollar contest to improve its recommendation algorithm. The researchers found that the set of less-popular movies a user has rated tends to uniquely identify that user. By comparing movie ratings on IMDB with the ratings in the Netflix data set, the researchers were often able to uniquely pair a particular IMDB user with a corresponding Netflix user. And that meant the researcher would instantly have access to all of the user's Netflix ratings, which Netflix users presumably expected to remain private. While movie ratings might seem innocuous at first glance, the authors point out that one's movie ratings can often reveal potentially embarrassing personal details, including a user's views on politics, religion, and homosexuality. This isn't the first time a company has released "anonymous" data regarding its users that turned out not to be so anonymous. Last year, AOL got in a lot of hot water when it released a data set of search queries that turned out to be quite easy to link back to the users conducting the searches. The lesson here is that companies should be very reluctant to release private customer data, even if they believe they have "anonymized" it. Anonymization is surprisingly difficult, and you can never be sure you've done it successfully; it's always possible that someone will find a way to link records back to the people they represent. Wherever possible, companies needing to release data should either aggregate it in a way that avoids revealing information about individuals, or they should carefully limit who has access to the data sets, to avoid having the data sets become publicly available. Simply stripping out the "username" field doesn't cut it.
Hide this

Thank you for reading this Techdirt post. With so many things competing for everyone’s attention these days, we really appreciate you giving us your time. We work hard every day to put quality content out there for our community.

Techdirt is one of the few remaining truly independent media outlets. We do not have a giant corporation behind us, and we rely heavily on our community to support us, in an age when advertisers are increasingly uninterested in sponsoring small, independent sites — especially a site like ours that is unwilling to pull punches in its reporting and analysis.

While other websites have resorted to paywalls, registration requirements, and increasingly annoying/intrusive advertising, we have always kept Techdirt open and available to anyone. But in order to continue doing so, we need your support. We offer a variety of ways for our readers to support us, from direct donations to special subscriptions and cool merchandise — and every little bit helps. Thank you.

–The Techdirt Team

Filed Under: anonymity, data
Companies: netflix


Reader Comments

Subscribe: RSS

View by: Time | Thread


  1. identicon
    Hallie, 30 Nov 2007 @ 3:47pm

    Sorry, you've lost me on this one. If I've read this correctly, the data set was NOT "de-anonymized", only a sub-set of it was. What percentage of the whole is it? I looked through their paper, but it doesn't seem to be mentioned anywhere. And the only ones who can be identified are people who made a public profile on IMDb who presumably don't mind being identified.

    I also don't agree with some of the conclusions to which the researchers jumped. For example, for one individual, they state "He did not like “Super Size Me” at all; perhaps this implies something about his physical size?" Or perhaps it implies that he thought the movie wasn't well-made, or that the story was cliched? They also state "Strong guesses about his religious views can be made based on his ratings on “Jesus of Nazareth” and “The Gospel of John”." If all they're going on is a numerical rating without any written opinion about either movie, the only conclusion they could reasonably make would be what he thought about the movies as movies.

    Sure seems to be a lot of noise without much substance.

Add Your Comment

Have a Techdirt Account? Sign in now. Want one? Register here



Subscribe to the Techdirt Daily newsletter




Comment Options:

  • Use markdown. Use plain text.
  • Make this the First Word or Last Word. No thanks. (get credits or sign in to see balance)    
  • Remember name/email/url (set a cookie)

Follow Techdirt
Essential Reading
Techdirt Deals
Report this ad  |  Hide Techdirt ads
Techdirt Insider Discord

Introducing the new Techdirt Insider Chat, now hosted on Discord. If you are an Insider with a membership that includes the chat feature and have not yet been invited to join us on Discord, please reach out here.

Loading...
Recent Stories

This site, like most other sites on the web, uses cookies. For more information, see our privacy policy. Got it
Close

Email This

This feature is only available to registered users. Register or sign in to use it.