Hello Codeforces,

I noticed something interesting about LeetCode’s external paste detection.

When you copy text from the LeetCode contest editor, it seems to attach a hidden marker like:

©leetcode

You usually do not see it during normal paste, but it can sometimes appear in clipboard history, for example with Win + V on Windows.

Now here is the funny part.

This marker seems quite easy to recreate manually.

So if someone adds the same marker to external text, LeetCode may still treat it as if the content came from the contest editor.

Basically, LeetCode sees ©leetcode and says: “Looks original to me. Approved.”

Of course, this is not very reliable. The concern is not that paste detection exists. Contest fairness is important, and nobody wants a leaderboard where the real problem is guessing who pasted faster.

The issue is relying on a marker that users can recreate. This can lead to possible bypasses, false positives, and a detection system that trusts a string a little too much.

A stronger system should probably rely on trusted editor events, internal metadata, or some verification method that cannot be forged by simply typing a hidden marker.

Because if the anti-cheat can be convinced by a small magic word, then maybe it is not anti-cheat yet. Maybe it is just politely asking people not to cheat.

I wrote a fuller breakdown here: Blog

Would love to hear what others think. Real issue, expected behavior, or just another frontend moment?