Given that parameter Psi = [ ( # of serious security flaws - 1 ) / ( # of running systems )^2 ] remapped in [0, 1]
Do you agree that, with a confidence level of 0.99, the correlation between the parameter Psi and Linux is stronger than with FreeBSD?
As "serious" is not defined and subjective and the number of running systems is not known/hard to estimate (Linux gets used in embedded environments too, where it will never show up in "server statistics") I can only say with 0.99 confidence level, that you are far off topic by now.
