You are allowed to compete with up to 3 accounts. Many data scientists use multiple accounts to experiment or compete with different types models. This is fine. In fact, the ability to manage multiple accounts will become a feature on the website eventually.
The purpose of the 3 account limit is to prevent spamming and information attacks.
Spamming is bad for the tournament as it adds noise and creates a poor UX for everyone else. For example, creating many accounts can take up spots on the leaderboard visually (even though this does not impact payouts). This may not always be malicious, but it is clearly negative for everyone else.
Information attacks is the attempt to access information about live targets that is not supposed to be revealed, and thereby gaining an unfair advantage over other competitors. Regardless of how effective this attack is, or how much of an advantage this actually yields, attacks like this is clearly degrades the integrity of the tournament.
Any user with more than 3 accounts detected will be given notice and 1 week to wind down to 3 accounts. After that, Numerai reserves the right to return any stakes, invalidate any payouts and to ban ALL of the accounts associated with the violator.
For security reasons, Numerai will never recover an account that is secured with MFA. This is to prevent others from impersonating and taking over your account. We recognize that this is not the best user experience, but because large amounts of money accounts can hold, we must prioritize security above all else.
Some users choose not to enable MFA at all. This is not recommended as it decreases the security of your account.
In order order to secure your account with MFA but not risk losing your account when you lose your device, you just need to save your recovery codes in a safe place. You can either save it in a password manager or on a piece of paper.