Dark Necro is a fanmade non canon character in the megaman universe.
After the defeat of Alpha by the hands of Megaman and lan in Megaman battle network 3, Scilab took two samples of Alpha back to Scilab for study. One was placed in storage, the other was experimented on by the scilab scientists. They found that infusing it with antiviruses turned it black in color.
"Scilab Journal XX/XX/20XX - Day 1
We did a couple of experiments on the peice of Alpha we recovered. We found that infusing it with antivirus data turned it a blackish color. It also seems stationary, as every time we look at it, it doesn't move."
"Scilab Journal XX/XX/20XX - Day 2
We finally named the experiment 'Project N3CR0' or Project Necro.We also have its first documented movement. We placed a dummy prog in front of it, and it moved towards it and devoured it. We beleive this stems from the fact that it is a part of Alpha."
A couple days later, the project suddenly went out of control, and escaped from Scilab. It hid in the undernet, wreaking havok by means of the viruses it produced from itself. Scilab scientists renamed it "Dark Necro." It also created a navi called Abyssman, who also seems to have the ability to summon viruses to his side in a matter of minutes. Many scientist navis have gone to capture Dark Necro, but almost all were deleted. Those who came back recounted a tale of a large blob with wings and hands that floated in the air that attacked them, almost instantly wiping out their fellow navis.