sudoku

during lunch break today, one of my co-employee showed a numeric puzzle and asked me to solve it. the puzzle is called sudoku. it sounds familiar to me, but i haven't tried solving any of this type of puzzle. so i asked what's the objective and how it's being played. after 30mins, i only filled 5 boxes haha instead of giving up easily, i still tried solving it becoz i don't want to end the day thinking about a simple puzzle i left unanswered. so hours passed and im still trying to solve it but it should be 1 puzzle = 10-30mins only. i finished solving the puzzle when we're just about leaving the office hehe so here it is, a sample of a sudoku puzzle. btw, the one i finished solving is a hard one hehe

obejctive:
Enter a numerical digit from 1 through 9 in each blank cell. Be carefull : Every row, every column and every square must contain only one instance of each numeral.

Warning: this is addictive