Interpreting Test Results
Sites like whoer.net or ip-check.info are unable to really understand and show the way anonymity is accomplished when using the Tor Browser. What these sites do, is check whether things like cache, cookies, and perhaps others are enabled. If so, they give better results, as to when they are activated.
In the case of Tor Browser, it has the goal to separate cache, cookies, etc. by browser tab. And things are deleted after closing the browser. The thing is, that instead of making it impossible for sites to safe data temporarily, this is allowed, as to make using most sites possible in the first place. To still guarantee anonymity, it is the goal to make everyone using Tor Browser appear the same, thus rendering tracking based on the things these websites show you pointless.
Making Browsers Safer
Browser fingerprinting defenses are not perfect yet. There are certainly too few volunteers working on seriously testing browsers and defeating browser fingerprinting. The key word is seriously.
If you are reading this page, then it is safe to assume being anonymous (less unique), and remaining so is of great interest. Users with a serious intention to research these issues are encouraged to assist in accordance with their skills. Testing, bug reporting or even bug fixing are laudable endeavors. If this process is unfamiliar, understand that about thirty minutes is required per message / identifier to ascertain if the discovered result  is a false positive, regression, known or unknown issue.
To date, none of the various leak testing websites running inside Whonix-Workstation were ever able to discover the real (external), clearnet IP address of a user during tests. This held true even when plugins, Flash Player and/or Java were activated, despite the known fingerprinting risks. Messages such as "Something Went Wrong! Tor is not working in this browser."  (from about:tor) or "Sorry. You are not using Tor." (from check.torproject.org) are in most cases non-issues. If the real, external IP address can be revealed from inside Whonix-Workstation, then this would constitute a serious and heretofore unknown issue (otherwise not).
It is unhelpful to ask questions in forums, issue trackers and on various mailing lists with concerns that have already been discussed, or which are known issues / false positives. In all cases, please first search thoroughly for the result that was found. Otherwise, the noise to signal ratio increases and Whonix development is hindered. Users valuing anonymity don't want this, otherwise this would violate the aforementioned assumption.
If something is identified that appears to be a Whonix-specific issue, please first read the Whonix Free Support Principle before making a notification.
- Please don't post any "Sorry. You are not using Tor." questions unless you are really sure it is not a false positive.
- Most likely a false positive.
- When you see this when using Whonix, probably everything is okay. You can make sure everything is okay if you want.
- https://check.torproject.org (
check.tpo) fails in some cases to detect Tor exit relays. It is a bug in
check.tpo, which The Tor Project should fix. Whonix can do nothing about it.
- If it is not your real external clearnet IP address, then there is no need for concern. You can find out your real external clearnet IP address by visiting some IP check website from your host or a non-Tor virtual machine.
- ExoneraTor is a website hosted by The Tor Project that indicates whether a given IP address was a Tor relay on a specified date. Use it. (using Tor Browser on the host)
- forum thread: https://forums.whonix.org/t/sorry-you-are-not-using-tor
- Forum thread, "ip-check.info some false values and confuses TBB users". (w)
- Possibly biased test service hosted by JonDonym that wants to spread JonDoFox and by extension sell premium accounts?
- ip-check.info is not Free/Libre/Open Source Software. (source) So someone else fixing it is unlikely.
Fingerprint Central differs from Panopticlick in that its dedicated to testing discrepancies between Tor Browser instances only. The code can also be run locally to help Tor Browser developers rapidly prototype defenses.
- https://amiunique.org/ - https://github.com/DIVERSIFY-project/amiunique
- [not yet released] http://browserprint.info/ - https://github.com/qqTYXn7/browserprint
- TODO test and document: https://fpcentral.irisa.fr/fp 
- The Tor Project task: Create our own instance of Panopticlick
- See tbb-linkability and tbb-fingerprinting.
- From a browser test website, in a log file and so on.
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This is a wiki. Want to improve this page? Help is welcome and volunteer contributions are happily considered! See Conditions for Contributions to Whonix, then Edit! IP addresses are scrubbed, but editing over Tor is recommended. Edits are held for moderation.