They are human-created programs who rewrite their own code to fix their own glitches and anticipate the user to become efficient.
Hardin, Schoppe's boss started working with his own Interrogative Agents and Peter's EPOs. This mix made the EPOs loose into the Internet and subsequently to the Source of the Real World. The EPOs gained access to the machines.
After Rain was killed, Peter entered an internet cafe and prepared e-mails with EPOs attached, to hacker and techie sites, networks and the Pentagon, and finally into Hardin's system. The moments when agents enter and shoot him, he notices on screen of his pod-self in the "machine world" and sees everything in green code. On his last thought, he sees the EPOs shoot into the distance of the green over-reality, hoping that some would awaken others into anarchy.