Threat hunting and threat intelligence has a special relationship. Think Sonny and Cher, Peanut Butter and Jelly, even cake and ice cream. They each stand on their own, some with great renown, but put them together and you have a whole that far exceeds the sum of its parts. And like the ouroboros, hunting and intel feed off of each other.
Start with a hunt. The purpose of a hunt is to find adversarial behavior on the network. You do this by forming a hypothesis (I believe the adversaries are trying to move laterally through my network using PS Exec), and then reviewing log information testing that hypothesis (what unexpected accounts are attempting type 3 logins on multiple systems, successful or not, spawned by the process psexec.exe). You find an anomaly and you document it, and then you run it down to see if it can be explained by regular user or system behavior. Should you find proof of adversary behavior, you document everything and you kick it over to incident response (assuming you are not also the incident responder). You then work to eliminate that adversary from your network.
Enter threat intelligence. They take the documentation from the hunt and analyze it. Was there a pattern in the remote login attempts? Did it target servers with a specific function? Was it the same user every time? Was it regular users or IT users with higher levels of access? Did it happen during certain times of the day indicating an adversary's working hours? What other processes did the compromised user account attempt? They work to see if it is all the work of one adversary or multiple.
Yes, multiple adversaries can be inside the same network, even doing battle with each other while assuming the other is legit sysadmin or security personnel. See the 2016 DNC hack after action report.
Threat intel works to build a profile, and that includes examining the kill chain from the recon stage to the point the adversary was discovered. The use the diamond model (http://www.activeresponse.org/wp-content/uploads/2013/07/diamond.pdf) shows tracking an adversary along the kill chain (https://www.lockheedmartin.com/en-us/capabilities/cyber/cyber-kill-chain.html) focusing on four points at each step in the kill chain: adversary, infrastructure, capability, victim. To analyze an adversary's attack, threat intel wants to be able to fill in all four vertices of the diamond. As they build a profile, they will see that an adversary may have undiscovered capabilities. An adversary may be discovering moving laterally with PS Exec, but how did they get on the network to begin with? How did they establish persistence? Building the adversary profile will create more questions. This can be compared against previous adversary documentation, or compared to information from external trusted threat intelligence sources.
The intel team takes these questions back to the hunters. Please hunt the history of the account usage, and look for the origin of anomalous behavior. Something had to happen (a process run, a file downloaded, a website visited) that preceded this anomalous behavior. The hunters then refine the hunt using the parameters given to them by threat intel team to flesh out more of the adversary capabilities. They return their findings to intel, who analyzes and asks more questions, the hunters refine the hunt even more, and this process is cyclical until the adversary tactics, techniques, and procedures can be assessed and documented.
Now, the results of this will be to create alerts (traps) should the adversary ever penetrate the network again. Then incident responders can use the adversary profile created by intel with information gathered from the hunters to contain and eradicate adversary presence with greater rapidity. These profiles can be used to track between similar but separate adversaries, and help paint a picture of motivation. This tracking of adversaries, and intent derived from behavior, can be documented and taken to leadership to say these are the types of organizations targeting our institution, and this is what they find valuable to disrupt and steal. We are better off directing our resources to elevate protection on this set of assets and people.
Documented evidence of intent and capability with a clear target make it easier for leadership to support a course of action. This continual process relies heavily on the coordination between the hunters and gatherers.
None of us is as secure as all of us.