Story Based Achievement
After Sequence 6 you will be back in modern day for a 3rd time. You will be asked to meet Melaine at the elevator. Soon after you will be given level 2 achievements. You will need to hack 1 computer, deliver the data back in the lobby and return to the Animus.
Once this is done achievement will pop. You can also enter all level 2 doors which if you have hacked all computers in level 1 areas should also get you the Ghost in Machine achievement.