There are particular circumstances, in which an IP anonymization via JonDonym is of little or no use at all. It is important to be aware of these situations in order to avoid being lulled into a false sense of security.

• Personal observation: Strong attackers, for instance secret services, are able to eavesdrop on the contents of your display by detecting its (or your computer's) electromagnetic emissions. On that way they are able to see what you are working on at the moment. They are even able to record and analyze the reflections of your glasses or your eyes.
• Standard Web browser: Normal Web browsers are configured so insecurely, that it is easy to obtain your IP address (and further data). You have to use a "hardened" Web browser like JonDoFox in order to protect yourself against it. Please bear as well in your mind to configure your PDF reader securely.
• Global observer: An eavesdropper who is able to collect traffic data before the first and after the last mix of a cascade may unmask users by computing correlations. Although Jondos is developing countermeasures (middle mixes, volume slices, mixing, burst proxy, dummy traffic,...) it can never be quite prevented. So, choose cascades with widely distributed first and last mixes.
• Data thieves within the last mix: It is true that the last mix is not able to track you with technical means. However, it can intercept data which you are sending to web sites unencrypted. The mix operator is liable for such infringements of your privacy. But they cannot be prevented technically.