IE Cookies
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The fact that IE8 doesn’t delete cookies upon telling it to (at least in my testing) until browser shut-down isn’t just bad for usability (and ho boy is it annoying when you’re testing) but it has other interesting privacy implications. Generally I tell people not to set the same cookie more than once. That makes it harder to use old XMLHTTPRequest bugs to download the cookie (which may otherwise be protected using HTTPOnly). But what if the cookie weren’t sensitive, but rather used for tracking?
If a site sets a unique cookie and the user clears cookies in IE8, that doesn’t mean that IE8 doesn’t keep sending the cookie (it’s retained in memory) - which means the site still gets it. If the site is trying to track the user they can simply keep setting the exact same HTTP cookie with an “expires” in the future to make it persist after the browser closes and voila! Even though the user thinks they cleaned their cookies, not for a moment was the cookie removed in IE8. Could be useful for banner advertisers or companies that need to do large scale tracking of users.
