I'm new here

Welcome to codeforces :)

what they are

hacking is to give a testcase that makes a solution to a participant fail(i.e Wrong Answer,runtime error, time limit exceeded)

who is the defender

the owner of the code that you try to hack

what does he do

he do nothing ,if his solution is absolutely correct then no one can hack his code

how to hack

On the dashboard, click the padlock icon for locking a problem (Note, that you can not send your solution for a problem after locking it). Then go to room results, where you can see roommates codes for the problems you've already locked (you can see a certain solution by double clicking on it in the room results table). After you've opened someone's solution, you can consider it and then hack it. When hacking a code, you're entering some testcase on which that code is most likely going to fail (it may be wrong answer, or running out of time/memory limit). When you want to enter a large testcase, you can send test generator instead of typing it. Test generator must be your program which produces a file with a testcase in it. After hacking a code, you can see hacking results. There are two possible outcomes: "Successful hack" — it means the code failed, and you're rewarded with 100 points for that. Otherwise, it's "Unsuccessful hack" (the code did not fail) and you get minus 50 points for that.

quoted from jskhirtladze

It's penetrating into someone else's computer.

:/

if i do not lock my code , than it is not hackable . am i right ??? or is it hackable ?? ( i am beginner )

After viewing the test case on which my code was hacked,the test case showed same output when I tried it on one of the correct solutions.Are there any other possible reasons of a code getting hacked ?

What kind of contest can be hacked? It seem like it include Educational round