Hi everybody!

Today I'm going to share an incident that I personally encountered during one of my contest. But before delving into the vulnerability, let's take a moment to understand the Codeforces hacking system.

Understanding the Codeforces Hacking System

Designed to maintain fairness and accuracy in competitive programming contests, Codeforces system enables participants to challenge the correctness of solutions submitted by their peers. This system involves submitting "hacks" against the code, where the system assesses the challenge and either confirms or rejects the hack.

Interesting Observation

But during one of my contest I was curious to know whether there were any Hacks for the problem A of that contest. While I was doing so I noticed some strange hackings.

I have simulated the incident in one contest to verify this. Have a look at THIS.

The main idea is: for a particular test case number, which is most probably not in the judging system i.e. 31 or 10067, a fake solution is printed and the solution either returns or breaks, since luckily the test case that is given is huge generally. The judge gives the AC Verdict but in reality this is WA. So, I found many users doing this kind of fake hackings. Most interestingly enough those who are submitting this kind of code are not rated. And those who are doing this kind of hacking are low rated. I guess we could easily guess something fishy. And I leave it to the respective community to decide.