Person of Interest question

 It's easy to wander into a new fandom these days, thanks to AO3... so the other day I found myself reading some wonderful Person of Interest fic, and since the show is available on Netflix I thought I would give it a go.  I managed to get halfway through the pilot episode and was so frustrated by what appears to be an enormous plot hole I stopped there.

So if there's anyone out there who can answer this I'd appreciate it.  The pilot shows that Harold and John are given Person X to watch -- they don't know whether Person X is a victim or a perpetrator, they don't know any reason why this person is a nexus.  But I know from the fic that a computer called the Machine is the supplier of Person X's identity.  The Machine must have an algorithm for deciding that Person X is a problem -- why can't Harold access the relevant data/evidence?  He's the programmer, right?

Is this another case where TV screenwriters demonstrate they don't actually understand what a computer is?  Or should I just be patient and tamp down on my frustration?