# Two Step Verification. 4 digits vs 6 digits

From a security level standpoint (such as Server, DataBase, Token Code, Authorization, Authentication, etc.) in regarding the Two Step Verification, usually Apple send a total of 4 digits security code vs Google send a total of 6 digits security code. What are the main differences?

For an $n$-digit code, if there is a single valid code and the code is generated at random, then the probability of a lucky guess is $10^{-n}$. That's 1/10,000 for a 4-digit code, 1/1,000,000 for a 6-digit code. These are usually acceptable figures when the one-time code is a second factor (usually complemented by knowing a static password or possessing a physical device); they would be grossly insufficient if the code alone was enough to access a service.