There are some things about this ideia to prevent the bad use:
1.Player who receive the verification code cant be attacked or receive any buff, debuff be attacked or receive cure.
2. There is a time limit of 10 minutes or more to answer verification code, but how about afk players? AFK status will deactivate time limit to prevent bad use in real players.
3. Verification code cant be used in duties.
4. Use of verification code to harm another players will receive a heavy punishment and should be reported via report harassment. Example: prevent player to attack hunts like Rank A or Rank S
5. You have 3 attempts to answer verification code, if you cant answer your account will be banned temporarily until a GM verify what's going on.