Why a stolen password may not be enough
When a service asks for a temporary code after a password, it is checking a second proof of access. The password shows that someone knows a secret; the code shows that they can also reach another channel, such as a registered email inbox or messaging account. A code that expires or can be used only once is harder to reuse later than a fixed password.
The protection depends on the two steps being meaningfully separate. If an attacker has only the password, the extra check can stop a login. But if the same password also opens the email account that receives the code, or that account is already compromised, the barrier is weaker. A code can also be tricked out of someone in real time, so it is a second check—not a guarantee that an account cannot be taken over.
The backup channel becomes part of the lock
That extra check creates a practical tradeoff: the account is harder to enter without permission, but the legitimate user must keep access to the second channel. A lost phone, closed email account, or inaccessible messaging account can interrupt sign-in too. Recovery options therefore matter; keeping recovery details current can prevent a security measure from becoming a lockout.
The key idea is that a password protects one door, while the temporary code asks for access to another. The arrangement works best when that second door is both secure and still reachable by its owner.
