When I go to https://check.torproject.org via TBB, I get a positive (green) result:

check.tp.o via TBB

But when I go there using another browser (non TBB) I get a positive (orange) result that says I am using Tor, but not TBB:

check.tp.o via non-TBB

How does check.torproject.org know I am using TBB? What implications does that have on my anonymity on the internet? What else can anyone (read: ISPs, governments, corporate IT personnel, etc.) know about me when I'm using Tor?

1 Answer 1


Tor check looks at the IP the request is coming from and checks if it matches the IP of a known exit node to check if you're using Tor. Tor does not attempt to hide the fact that you are using Tor from any end servers, it just hides who you are.

To see if you're using the TBB it checks that your user agent matches that provided by the latest TBB (Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Firefox/24.0 at this time). This means it will throw a false positive if you're using a version of regular Firefox with that user agent string.

ISPs, Governments, and other middle men are more likely to inspect network traffic to determine that you are using Tor (this does not mean they know what you are doing over Tor, just that you are using it).

  • Just verified it by changing the user agent of a regular firefox :)
    – amyassin
    Nov 26, 2014 at 8:25

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