I'd leave them an "infinite zip file" with a very interesting name "creditcardnumbers.zip" or "bankdetails.zip" http://research.swtch.com/zip[^]

that's why I name my variables a,b,c,d,e,f etc. never any room for confusion as to their purpose. I can even recycle them later on in a method and save on stack space :-)

I'm from the old school where we used to code in assembly language. Machine language is completely reversible, just a little harder. How do you think hackers go about removing the copy protection from commercial software? Or virus-killers go about understanding what a virus does? The determined will be always able to figure out what your app is doing.

Netbeans (free) has a UML tool