I don't understand:
I don't see how "certain" and "may have been" fit into the same sentence. Seems to me either that (1) you must be certain he was a hacker, or (2) you guess he probably was a hacker.
But the two alternatives seem mutually exclusive. So which conclusion should we accept?
I am certain he is a hacker, there is no doubt, he even wrote a book about it in the 90s. I am also certain he was a foreign operative, if anything, an undeclared tool. “may have been” is where the guess is, is he still an operative for a foreign government, is he an operative of non-governmental powers (Soros or others) or is he a rogue doing this on his own? Considering his influence, history, and what he is able to achieve, we can almost certainly eliminate him being a rogue.