I got this message today from system:

Attention! Your solution 295598611 for the problem 2040C significantly coincides with solutions fbrunodr/295598611, gunjackk28/295637944. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://mirror.codeforces.com/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked.

I use my personal laptop to code (so this is not unintentional leakage) and haven't provided my source code to anyone. The only thing I can think of is that someone abused the hacking feature of codeforces to leak my source code to a friend (as leaking their own source code would be to obvious, right?). The user who copied my code is gunjackk28 from India. He submitted the problem in the very last minute of the contest (01:59:05). Checking my room in the contest, only 3 other people got AC on the copied problem (problem C); one of them, HardikChoudhary, is also from India and got AC at (01:55:53), just 3 minutes before gunjackk28 submitted an exact copy of my source code. I think this is highly suspicious and should be investigated.

I never violated a single rule in codeforces and now I am being threatened to be blocked/banned because someone else cheated, this is completely unfair. I think the best solution in this case would be to remove the hacking during contest feature, as has already been suggested in another post.

Just before someone suggests it might be a coincidence, it is impossible in this case, as I use a highly specific .cpp file as template (which can be found in my GitHub). You can check the submissions here and see that there is no explanation other than the guy simply copied my source code:

My submission: https://mirror.codeforces.com/contest/2040/submission/295598611

gunjackk28 submission: https://mirror.codeforces.com/contest/2040/submission/295637944