FW: Fingerprinting timezones

John Haxby john.haxby at oracle.com
Thu Aug 11 09:17:01 UTC 2011

On 09/08/11 05:16, Olson, Arthur David (NIH/NCI) [E] wrote:
> The problem I would like to solve is that of having to ask a user of a
> web-app for their timezone. While there is no way to directly query
> for the user's timezone, the javascript engine in their web-browser is
> capable of telling me the offset from UTC at any date.
> It seems like, by selecting some number of dates to query, I should be
> able to gather enough information to uniquely identify any given
> timezone (or at least make a very good guess for a large proportion of
> the user-base).
> Before I embarked on doing this, I wanted to ask if anyone has seen a
> similar attempt in the past? Are there some "gotchas" that mean that
> this isn't actually as feasible as I naïvely hope?

 I happened to come across this today:

The code and an explanation is here:


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