You get a good amount of XP for hacking terminals in Fallout New Vegas so it pays dividends to do it properly and correctly identify passwords. Check out this guide for tips on how to hack successfully.
First up, in order to be a successful hacker, you need to know what you have to do to solve the password.
When you activate a hackable terminal you’ll be presented with a list of words mixed in with random characters. All of the words are the same length and one of the words is the password. You have to select a word by clicking on it. Upon selecting the word you’ll see something like “2/8” displayed on screen. The left hand digit refers to the amount of letters that are correct in the word that you choose. The second digit refers to how many letters are in the word. This second digit remains constant throughout your guesses because all words in each puzzle are of equal length.