I've noticed when updating a blog, that sometimes refreshing the page won't actually fetch it again, because it is still in the cache. Now, even when I open it in incognito in that same browser(say Chrome), it still uses the same cache, at least for some time. My understanding is that the site can "tell" my computer how long to store the page before fetching it again. So, say I set up a site that dynamically puts in the time and date, (or a unique code), into the page in a hidden field, and on loading, sends that back to me using Javascript or whatever. So I can tell if my site was browsed before by checking when I sent that code or what the time is, even though the browser is now in privacy mode.

Would this work, and if not, why not?


Yes and this is by design:

The point of incognito mode is not to prevent server side tracking. The whole design is about not leaking information on the client (about visited sites).

This comes from the Chromium team - look at Comment #8 I believe other browsers work similarly.

Some of the ways a site could do this:

  • ETags - these are cache directives. If the page has been cached in normal mode, then these cache entries are available in incognito mode.
  • IP address
  • Browser fingerprint - screen resolution, installed plugins, etc.

You may be able to get better privacy by using Privoxy in combination with incognito mode.

  • This is leaking information on the client about visited sites. The website can tell if I have visited it in my browser without privacy mode. And it might even be able to see other sites via hidden frames or whatever
    – ike
    Dec 12 '13 at 17:38
  • @ike In which direction is it leaking information? From normal to incognito, or the other way round?
    – paj28
    Dec 12 '13 at 17:40
  • From normal to incognito.
    – ike
    Dec 12 '13 at 17:45
  • @ike leaks from normal to incognito are allowed - this is made obvious because you have your normal address bar history available in incognito mode. If you find a leak the other way then you should definitely report it to the Chromium team.
    – paj28
    Dec 12 '13 at 17:48
  • I don't think so, I as a user can access history in Incognito mode, but the website can't. My method would allow them to.
    – ike
    Dec 12 '13 at 17:49

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