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15 G

To get this you have to hack 25 terminals.

Here is a list of about 35-40 terminals you can hack for the achievement. There are more but not nearly as many as in fallout 3. I'm guessing its maybe around 50 total terminals.

Some of these require a high science level and I think 2 of them require 100 on lockpicking to open the door to the terminals. Both of those skills at 100 are recommended for the story anyway so I'd make sure you have those both at 100 before even hitting all these places :

Goodsprings - Bar
Goodsprings - School
Primm - Bison Hotel
Sunset Sarsaprilla Factory - (2) inside the building
Crimson Caravan - Main office building
Camp Golf - (2) in the resort house 1st floor
Black Mountain - (2) in the main radio tower part & (1) in the prison building.
Reppcon HQ - (3) on the 1st floor, (3) on the 2nd floor & (1) on the third floor. I found a total of (7) in this building.
Camp Searchlight - (4) are located on the 4 turret placements in the main city. This camps location is near the bottom of the map towards the center. There is radiation in the area as well so have some Rad-X or Rad-Away handy while your roaming through the place.
NCR Headquarters on the vegas strip (3 Total) - (1) in the Military police HQ & (2) in the NCR Embassy
Helios One (1)
Vault 3 - Living Quarters (2)
Brotherhood of Steel Hidden Valley Bunkers (2)
Hoover Dam (1)
Vault 21 (1)