But what is more probable? The number of known NSA backdoors is greater than zero, but is small compared to the number of known lazy or sloppy programming mista

But what is more probable? The number of known NSA backdoors is greater than zero, but is small compared to the number of known lazy or sloppy programming mistakes. That said, the likelihood that a potential exploit will be used by the NSA is very close to if not exactly 100%. You don't have to inject a vulnerability into a system when there are more than enough unintentional holes already.