Please add option to increase secure code length

Hi,

I'm subject of targeted attack likely related to what I'm currently working on. It's nothing related to politics or ideological matters but I don't want to go into details, since it's more or less secret, so those attacks are not just some random trolls since I wasn't public about that anywhere and didn't share my email either.
Anyway, even if those attacks are not due to what I'm doing they are certainly targeted because they didn't happen at all in past and now they happen multiple times from different countries as you can see in screenshot below. It might be the same person using VPN but it's definitely not a random guy who misspelled his email.
Having said that I would really appreciate if you would add option to increase security code length from current 6 digits to something more serious like 24 digits.