Fiddler on the what?
Fiddler on the Root.
One of the primary goals of hacking a system is to try and get "root" access to the computer. A root account has no restricted functionality and can perform privileged operations. If this type of account can be exploited, the potential damages are exponentially magnified. In order to get this access, a significant amount of trial and error (fiddling) with the application is necessary. Together, these terms form our play on words based on the musical Fiddler on the Roof by Jerry Bock.