When a software engineer discovers a secret network that monitors and manipulates the general public, he has no choice but to hack and control the assassin sent to kill him.

On fire Knightrider1984!

This one did not work as well for me because the narrow objective of hacking / controlling the assassin is not the issue he ultimatley has to deal with, just a minor obstacle on the way. The issue is dealing with the secret (uber-powerful) network.

What I understood from the logline is that he has an assassin after him because he discovered the network. Is that correct? I think dpg is totally right when he says you need to clarify the causal link between the two things to avoid confusions like this! Anyway, it seems like a good idea!

Even if he hadn't discovered a secret network, yada, yada, he would still have not choice but to do something about the assassin because it's his life on the line, right?

As written, the threat to his life seems casually independent of the secret network: He discovers a secret network; oh, and there's somebody out to kill him.

What the causal link between the network and the assassin?

Hi, sounds like a good idea. It might be useful to try to shorten the initial explanation of the master plan. Do we need to know everything? It takes up a lot of your precious words. It might be good to get more of sense of his personality , and to try to make a real contrast in personality between him and the assassin. Also, it might be useful to get a hint at why the assassin has swapped sides?