The Code by Aduro(you can read it on fanfiction.net).
It's part of The Code Series: The Code, The Code Breaker, The Decoding, The End Code.
The last one is still being written. If you decide to read it, you'll find an amazing story, some fluff, some angst (Draco gets quite a lot of grief and angst coming his way but he also gets a friend - Bill Weasley, there's also some fluff). You may read only the first story, or all of them. Anyway, it's an unique and very captivating story.