How does Buzzfeed "Pound" work?

A week ago, Buzzfeed announced a new viral tracking tool called "Pound" (Process for Optimizing and Understanding Network Diffusion). While marketers and webmasters are currently used to view social traffic in aggregate codes per source, Pound promises to help us visualize the actual exchange of personnel between people and the traffic received at each stage ... sorta, apparently , the tool is unable (or unwilling to) map individual users to their respective node on the network:

Pound does not store usernames or any personally identifiable information (PII) with shared events. Each node in the shared graph is anonymous. We cannot figure out who the user is by looking at the graph data.

Interesting. I believe Buzzfeed prevents this anonymous one from crowding out complaints when the company uses Pound to sell ads. More interestingly, a hint from Buzzfeed engineers on how this tool works:

Pound data is collected based on an oscillating anonymous hash in the partner URL as a UTM code.

How it works? Does the UTM code change every time a link is split or published? I don't understand how this is possible. If not, how is it possible?