You will receive the Hanar Diplomats mission in a message on your private terminal. Jondum Bau will ask you to meet him on the Citadel to investigate the possibility of one of the diplomats being an indoctrinated Reaper. He will have obtained this information from none other than Kasumi Goto from one of Mass Effect 2’s early DLC releases. If you recruited her and completed her loyalty mission in that game, your rewards for this mission will be even greater now.
Head to Commander Bailey’s office to find Jondum waiting for you outside. Speak with him and he will ask that you head to Spectre Requisitions and investigate the terminals. Head into the Embassy and look to the left of the rows of chairs to the side to find the first terminal on the wall. Now go to the elevator and ride it to the Docks: Holding Area floor. The other two terminals will be here. The first is right out of the elevator. The final terminal is towards the back of the area. Look for Bay E28 and you will see the terminal on a wall next to some chairs. Head back to the other terminal and you will obtain the final piece of information needed to make your case. From here, you will confront the hanar who has been working for the Reapers. He will tell you that he has uploaded a virus to the defensive network in order to allow the Reapers safe passage.
In an attempt to stop the virus upload, Jondum will be wounded. Shepard will continue on without him, activating the computer. At this point, a prompt for a Renegade action will appear. Think carefully about this one. Complying with the prompt will abandon the computer in favor of saving Jondum. This will, of course, condemn those on the hanar’s homeworld to die in the Reaper invasion. Either way, you will obtain a war asset. If you save Jondum, he and his team of Spectres will join in the battle with you. Otherwise, the hanar homeworld will pledge their strength to your cause. If you helped Kasumi out in Mass Effect 2, however, you won’t have to make the choice, as she will swoop in to stop the virus even as you save Jondum. Otherwise, there is really no “wrong” way to do it. When you complete the mission, provided you helped Kasumi in Mass Effect 2, she will also join your team in the form of a war asset.