Well, it is located here: YOUR_MATHEMATICA_LOCATION/Configuration/Licensing/mathpass
At least on Linux, it is so. I am not sure about Mac and Windows case.
Actually, I think Wolfram Research uses a very weak way to protect their copyright. The password file looks like this:
I think Mathematica did great scientific visualization job. So, if you want to make your biological paper more fancy, maybe you should try my combination: Python (SciPy) for bioinformatics computing + Mathematica to attract girls eyeballs - Just try
ProteinData["A2M", "MoleculePlot"]and then rotate the 3-D structure of protein and then ask the girl next to you "Wanna have dinner with me some time?"
A weak point of open source software is visualization while a killer point is their great performance. If you combine open source solutions along with commercial solutions, you can publish great papers while having a pretty girlfriend - This is not a scientific conclusion. LOL.