In the GTA Online heist setup mission, Humane Raid - EMP, Agent 14 mentions that they found out about the EMP on the Dark Net, when the military tried selling it and some other military equipment on there.
The Dark Net is a reference to the real life Dark Web, a hidden part of the internet containing illegal and sometimes inhumane features not allowed on the normal internet. It can only be accessed via the infamous Tor Browser. Some of the illegal activities include drug trafficking, mutilation, arms smuggling/deals, child pornography, and ordering assassinations, the latter being what the military were doing.
The Finance and Felony DLC may add to this Easter egg. In the trailer for the DLC, a container which says Human Organ Transplant can be seen on a shelf in a warehouse, which can be a reference to Human Organs.