Re: how does host B know that its visitor is the one that visited host A?

On Aug 12, 2011, at 8:11 AM, Jonathan Rees wrote:

> Probably everyone knows this but me...
> I shop at (or somewhere) for a London hotel room. Later I
> visit and see an Expedia ad for London hotel rooms.
> I visit in a different browser (same computer & IP
> address but Safari instead of Chrome) and instead get an ad for
> magazine subscriptions. Apparently the Guardian can tell my two
> browsers apart somehow - it's using more than just my IP address to
> decide what ads to show me.
> How does this work? I.e. what are browser instances doing that leaks
> their identity to servers? Is it just a lucky guess based on
> User-agent or something?
> (a propos our privacy & tracking discussions)

For the cross-browser tracking they're likely using Flash Local Shared Objects. The fact that the info is shared among browsers is most likely a happy accident, the intent is more to have a "cookie" that doesn't get cleared when browser cookies are cleared and also often bypasses regular browser cookie controls and privacy modes.


Received on Sunday, 14 August 2011 05:49:13 UTC