If we find that your account's security has been compromised, we will immediately lock the account down to prevent any further damage being done to it and prevent any changes to your login information being applied. A locked down account cannot be logged into using the game client or the forums and no changes can be made to such an account's password (except through the "Forgot Password" e-mail method), associated e-mail or account name and no further purchases can be made using said account.
When you attempt to login, a TennoGuard 2FA code will be sent to the e-mail attached to the account in order to unlock it for play, however trading restrictions will remain in place until you contact Support.
While locking it down has secured your Warframe account, please be aware that at the minimum the player who accessed your account has knowledge of the password you were using! If you wish to obtain information on how your account information may have been compromised, an excellent tool that you can use is Have I been pwned.
Now that your account has been secured from further access by an invalid party, please contact Support and we will assist you with restoring your account.