After Educational Codeforces Round 120, I went through all the successful hacks and found some suspicious hacks. A couple of submissions of problem A by an account called SIMON_MOLODETS have been successfully hacked. I got curious and viewed his code, and this is what I found: 140819355 140819499 140819706 140819908 140820020 140820234 140820399 140820592 140820839 The following is one of his submission:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
int n;
cin>>n;
if(n!=67){
for(int i=0;i<n;i++){
    int a;
    int b;
    int c;
    cin>>a>>b>>c;
    if(a+b==c or a+c==b or c+b==a) {
    cout<<"YES"<<"\n";
    continue;
    }
    if((a==b and c%2==0) or (c==b and a%2==0) or (a==c and b%2==0)){
    cout<<"YES"<<"\n";
    continue;
    }
    else{
        cout<<"NO"<<"\n";
    }
  } 
}
else{
    for(int i=0;i<67;i++){
        cout<<"NO"<<"\n";
    }
  }
}

All the submissions above are almost identical. The only difference is the 8-th line. He used if(n!=67) to deliberately output a wrong answer on specific inputs that did not appear in the pretests, in order to trick the judge believing the code is correct, and then use another account to hack the code with the specific inputs.