A new form of cheating I speculate might be happening in rounds with points for hacking like today's CF Round 770... The procedure is as follows:

1. Create an alt account.

2. Write the correct solution for a problem, say problem A.

3. Assign an incorrect answer for a particular test case which you speculate might not be in the pretests and write the correct general solution and submit and get AC.

4. Go to your original account and hack it using that particular test case and get 100 points.