There are several methods of preventing Passive traces from coming back to you. Here are some suggestions.

First, it is best to delete any logs left behind on the target machine. This is not always possible though, (you may be forced to disconnect quickly) and it is not always successful.

If you can establish one link in the chain on a computer that you can access easily, you can erase the logs on that machine after every call bounce. This requires admin access on a low security system. Academic systems are ideal for this due to the low consequence if caught.

Another common trick is to route through a financial or government system. These companies are typically very resistive to opening their logs to other agents, due to the sensitivity of their data.

Further Data

If you want to be extra secure, then make sure to route through a low security system that you can gain admin access on (to delete records), and also a government machine so that it will make tracing through that system much harder. If you are really paranoid about being caught, then you can always delete log files on several machines and route through several government systems when attempting a hack.