Not much is known about Carrion apart from that it was stopped and listed as a failed project. Nolan Ross is presumed to have written the program, or been deeply involved in its creation due to him having the code needed to finish it stored in his mind. Carrion is a secret with very few members of NolCorp knowing about it. It is unknown why this program was created in the first place.
Whilst its not known exactly what the program can do, Nolan has stated that it is able to turn off the entire Manhattan power grid in a micro-second. Also, in Illumination, he uses it to hack a website, suggesting that it is a hacking tool. The only copy of the program that still exists is stored on a black portable hard drive though this was revealed to be incomplete with the code needed to make it work is stored only in Nolan's mind for safety.
It is presumed to still be a dangerous piece of software that could cause some sort of disaster due to the Americon Initiative attempts to get hold of the copy. It is presumed by Emily and Nolan that the Initiative are going to use it to cause another disaster or terrorist attack.
In "Engagement", the lights across New York City and as far as the Hamptons suddenly turn off. While most think it's a regular blackout, Nolan, Aiden and Emily realize that the Intiative have activated Carrion. The episode ends with Emily saying "it's started".
In "Truth, Part 1", after the power comes back on, it's revealed by the news that the program used was uploaded from servers in Tunisia and Bahrain, where Helen had had Grayson Global invest in companies.