"Do Not Track": All or Nothing?
According to
press
reports,
some Internet marketing companies are starting a "Do Not Track" list,
a way to opt out of tracking cookies. It’s a good idea, but there’s
a downside: using this scheme can hurt your privacy unless you’re
very careful.
Internet marketers typically track people via
cookies. A cookie is a small amount of text stored on your
computer by a web server; it lets the server know you’re the same
person (more precisely, you’re using the same web browser) who visited
the site some other time. Some cookies are used to track your preferences,
such as what sort of web sites you visit or articles you read; this is
used to tailor ads to your (perceived) interests.
One of the best explanations of cookies and advertising can be found at
Doubleclick’s
FAQ.
(Doubleclick’s
privacy
policy disclosure
is one of the best out there.
This is quite ironic, since years ago they were
roundly criticized for their privacy practices.
On the other hand,
very few people know to check that site, since most people don’t even
know it exists.)
You can see how this works by connecting to
my cookie test server,
which I’ll leave running for a few weeks.
A typical "Do Not Track" option works by letting people download
a special cookie. Doubleclick’s
opt-out
service does just that:
Presumably, the AOL version would be more complex, because it will let
you specify your interests. That is, it’s intended to permit targeted
advertising but without tracking.
The problem is that today’s best way to avoid tracking — regularly
cleaning out your cookie collection — will delete the "no-track"
cookies. (Doubleclick even warns about this.) Users will thus be
faced with a choice: defend against everyone, by frequently discarding
all cookies; defend against the more responsible marketers, by using
their no-track cookies; or trying to remember to be selective about
discards and/or recreating many different no-track cookies very frequently.
None of these options sound appealing.
Update: a
New
York Times blog
has noted the same problem. It refers to some technology developed
by Tacoda to permit preferences to
persist even if cookies are deleted. It isn’t clear to me what that
technology is; Tacoda and its subsidiary,
Advertising.com have web
pages on cookie-based opt-out. Perhaps it uses a
Flash cookie?
Flash cookies are just about as useful for tracking people, and they’re
seldom deleted because most people don’t know about them.
