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RE: Action 32 -- Proposed language for site-specific exception

From: Jules Polonetsky <julespol@futureofprivacy.org>
Date: Thu, 10 Nov 2011 06:09:53 -0500
To: "'Aleecia M. McDonald'" <aleecia@aleecia.com>, <public-tracking@w3.org>
Message-ID: <018501cc9f99$46376570$d2a63050$@org>
Studies about self reported user activity around blocking cookies seem to
range widely.  The statistic I cited is based on a review for me by an ad
serving company of their log-files to determine how many users did not have
a cookie from this adserver.  (They have 90 plus per cent reach of the US
population).  Approximately 30 per cent did not have a cookie from this ad


So this is because of a number of factors - some users were blocking
cookies, or deleting them upon closing their browser, some may have just
recently cleared cookies, some may have just bought a new computer, or some
may have had so many cookies set that earlier cookies were discarded.  The
takeaway I think is that approximately 30% of users are initially
unrecognized by a third party tracker.


From: Aleecia M. McDonald [mailto:aleecia@aleecia.com] 
Sent: Wednesday, November 09, 2011 5:42 PM
To: public-tracking@w3.org Group WG
Subject: Re: Action 32 -- Proposed language for site-specific exception


Here I am summarizing a conversation that Rigo, Thomas, Karl, and I had last
week, to share it with the group. 


A few notable problems with opt-in cookies are similar to the issues that
make a DNT header attractive in the first place. Namely:

            - Not all user agents support setting cookies

            - Not all user agents are terribly fingerprintable, and these
are often the same as not supporting cookies (for example, a not-so-smart

            - Many users either block or manage (that is, some how delete)
cookies. In Princeton, Jules suggested this may be something like 40% in the
US and 50% in Europe. This is from memory; I leave Jules to correct me if
I'm off.


And for me the biggie:

            - The users who have DNT on (which is a superset of users who
will opt back in) are far more likely to be among the subpopulation of users
who manage their cookies. Designing a solution that is least likely to work
for the population most likely to use it seems like a problem to me.


So while I very much agree with Nick that having a standard way to add
site-specific exceptions is highly desirable, I hope we can find a mechanism
that works better than cookies. 




On Nov 9, 2011, at 2:26 PM, Nicholas Doty wrote:

One advantage of a tech-specific requirement (placing an opt-in cookie)
would be the relative simplicity for users to clear all of their tracking
opt-ins - just clear your cookies. If some sites use fingerprinting and
other sites use localStorage and yet others use cookies to store a user's
opt-back-in status, then a user would have to manually manage on a
site-by-site basis if they decided they wanted to opt-out again.


We might be able to address this concern with some variation of the Tracking
response header / well-known location such that user agents could detect
when a user is being tracked because of an opt-back-in and give the user a
pointer on how to clear it. This is also an advantage of the
user-agent-managed list of site-specific exceptions: the user agent could
make it easy for users to see and modify the list of site-specific





On Nov 9, 2011, at 8:14 AM, Shane Wiley wrote:

Thank you John - helpful starting point.  I'd suggest we not assert only a
cookie as the "exception" memory mechanism but a recommended one.  It could
be equally viable and appropriate to store this information in a
registration key, a browser setting, or some other technical mechanism.


- Shane


From: John Simpson [mailto:john@consumerwatchdog.org] 
Sent: Wednesday, November 09, 2011 8:00 AM
To: Aleecia M. McDonald; Nicholas Doty
Cc: public-tracking@w3.org Group WG
Subject: Action 32 -- Proposed language for site-specific exception


Proposed language for a site-specific exception using a cookie:


When a DNT enabled user agent grants a site-specific exception, the site
places a site-specific opt-in cookie on the user agent allowing the site to
respond as a First Party.  The DNT header must remain enabled so that if the
user returns to the site, both the user's general preference for DNT and the
site-specific exception will be clear.  This could enable the site to
provide a higher level of privacy than if DNT were not enabled, but less
than if the exception had not been granted. Opt-in site-specific exception
cookies should expire within three months, enabling the site to determine
periodically whether the user intends to continue to grant an exception.



John M. Simpson

Consumer Advocate

Consumer Watchdog

Tel: 310-392-7041



Received on Thursday, 10 November 2011 11:10:27 UTC

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