In The Matrix Reloaded (2003), Oracle says to Neo about hacking programs:
Oracle: The ones doing their job, doing what they were meant to do, are invisible. You'd never even know they were here. But the other ones....Well, you hear about them all the time.
Neo: I've never heard of them.
Oracle: Of course you have. Every time you've heard someone say they saw a ghost or an angel... ...every story you've ever heard about vampires, werewolves or aliens...is the system assimilating some program...that's doing something they're not supposed to be doing.
Neo: Programs hacking programs.
What does "they" in "they're not" refer to?