There is one fact appearing eventually after these considerations.
When I first heard the name of “Shadow brokers”, I thought it was quite weird, as it did not mean anything in English. Originally, I assumed there was an organization called as “Shadow government”, whose brokerage was named as “Shadow brokers”, or something like that. It means there is something behind the name, which should generate the name of “Shadow brokers” in the end. That should be a key to near the criminal, I thought originally.
However, this name comes from the Japanese word, therefore this “shadow” means “underground”. They are claimed to be underground brokers, though “shadow” reminds an espionage in Japanese, which comes from “ninja”.
In Japanese sense, when you disguise yourself to live, it is said to be living in the shadow. This sense is quite matching to the ninja, and then there were several ninja stories whose main characters had been named after the shadow for many decades. That is why the shadow has been commonly associated with the ninja in Japan.
They were espionages in the past days, hence the shadow is associated with the spy as well in Japan. That means “Shadow brokers” sounds more like “covert brokers” by English.