I use a VPN service that provides a pool of IP addresses, I clean history/cookies/etc - all the browsing data before a session.

Regardless, when I type in the search of one particular search engine, I begin to receive personalized suggestions that, for sure, are based on my previous queries as these suggestions are very rare and surely cannot be common.

I use FireFox as a browser, with standard settings and without addons. I am not using any accounts like a Google account.

How can either FireFox or the Search Engine know my history under the aforementioned circumstances?

And how can I make my VPN sessions unique (providing they do have unique IPs) for web-servers?

1 Answer 1


If you are truly clearing all the local records when you close the browser, are not logged in to any accounts and are connecting through a VPN, then it is possible they are using information your browser itself reveals about you to guess at who you are. Certain information can be provided by a browser to the server.

Things like available font lists and lists of installed plugins can be very unique and result in being able to detect your system. It's also possible that you haven't killed all local records. Browser cookies are not the only way to store information. Various plugins (such as Flash, or even built in features of the browser) can provide additional storage capability or track what you are doing locally.

Are you sure that you do not have any of Firefox's built in search optimization stuff turned on? Firefox has sync features that keep an online record of your activity to allow it to follow you from one device to another. This could easily be responsible for the observed behavior. There can also be other more stealthy local records such as storing cookies via Flash.

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    "If you are truly clearing all the local records when you close the browser, are not logged in to any accounts and are connecting through a VPN, then there should be no way for a web server to recognize you between visits." Basically you are right, but practically it's a different story: panopticlick.eff.org
    – Luc
    Commented Apr 23, 2013 at 7:25
  • @Luc disturbingly correct. And Don't forget things like 'super cookies' (flash cookies etc)
    – NULLZ
    Commented Apr 23, 2013 at 10:00
  • @D3C4FF - that would be part of clearing all local records. Clearing all local records is more than just wiping history and browser cookies. (Technically things like browser tracking are also another similar feature. I will add flash cookies as another possibility in my answer.) Commented Apr 23, 2013 at 13:34
  • @AJHenderson yeah, i guess. But just going Ctrl+shift+del in browsers doesn't clear them. It depends on how paranoid and how serious alex is about cleaning up after himself. A step by step guide on what alex does to cover tracks would assist i think?
    – NULLZ
    Commented Apr 23, 2013 at 13:38
  • @Luc - very intersting. Mostly seems like the font and plug-in detection are the giveaways, though I'd hazard if you have default system fonts and plugins are disabled, then it would greatly limit what could be detected like this. I'll update my answer to reflect this. Commented Apr 23, 2013 at 13:45

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