in one of the first missions, when you have to slide down of the bars and kill a guard, then u have a keypad in front of u with flashing numbers. I don't know what to do over there. Can somebody help me please...
You don't have to KO/Kill that tech. If you wait he will eventually move away.
Neway, to hack the keypads in SCDA - there are four columns of numbers rushing by - scan them until you see a number stop. Move quickly to that number and tap 'A' and continue this until you lock in all four numbers. It seems difficult at first, but once you get used to it it's very easy.
Remember that your 'cursor' "wraps" the screen so that if you're at the left column and one on the far right locks, you can move left to get there more quickly!
