From the start of the game, do the following things as soon as you gain control of the character. DO NOT pick up the school badge from the middle drawer of the desk, even when the computer becomes annoying telling you to do so. Not doing so allows you infinite time.
Stuff in  brackets are actions.
Stuff without  brackets are things you need to type into the computer.
[Put phone receiver on top of modem to the left of the keyboard]
[Turn on PC by pressing the red button on the keyboard]
[Input name of choice]
Kill Process 1
Kill Process 2
Kill Process 3
Kill Process 4
[Highlight Brute-Force attack by pressing DPad-Up four times, then press A.]
[Whilst The Hack is in progress PRESS NO OTHER BUTTON. Just occasionally wiggle the Left stick so that your controller does not die. This is to stop the game glitching the hack.]
This will take 600 in game minutes, so you'll be waiting for about 15-20 minutes. Once the hack is successful, the achievement will unlock. Also, no, there's no way to turn off the annoying computer voice telling you to get the telephone number for your school. Just ignore it. For all of these hack achievements, it's so much easier to do them BEFORE picking up the schoolbadge, as two things are advantagious here: 1) You don't get tired. 2) Your mother will not bug you with meaningless annoyances like 'reading a book'.