The cheating method involves creating two separate user accounts, primary and secondary. The primary account submits the correct solution to the problem but the secondary account submits a slightly modified version of the code, which includes a strategically placed if condition that does not do any problems in the pretest but when a specific input is entered causes the code to fail. Then the User hacks his own solution from the primary account.
This is a very good loophole that these people have found and I came across it in Codeforces Round 878 (Div. 3) check out these few submissions that have been hacked:-
Now as shown in the image why do think the condition (s == "farazf") is required? did the question ask him so? I don't think so because I gave the contest myself. This condition is used to exploit the vulnerability of the system and get sweet points by hacking the solution.
I just wanted this to come to light :) If it was already general knowledge among the people then please ignore this post or you can upvote it so that it reaches the organizers so that they can take some action regarding it.
If there are already some rules regarding this loophole and please do let me know so that I won't try it :) Special thanks to Ai for writing the title. So what if AI cannot solve the CP question doesn't mean it is useless :)