I'm Spanish too, so hopefully I can explain. The problem is that everyone treats the SSN as if it were a secret number known only to you, so they use it as both an identifier and an authenticator. In Spain, however, most people know to use the DNI number as just an identifier, using other methods (most typically, physical presentation of the ID card) for authentication.

A social security card is not identification. It has no photo on it. Yet, as others here are saying, many organizations use the number itself as identification when it was never intended for that purpose.

Perhaps the answer lies in the fact that the US has no national ID. IDs are issued at the state level and the details vary from state to state. This helps make it easier to forge identification because locals will not be familiar with the standards of all fifty states. So, due to the lack of a national ID, we use the federal social security number in a manner it was never intended to try to fill in this hole in our system.

The political organization of the US is a little bit like the EU rather than a country per se. Each state is a little bit like a separate country in some ways. There are overarching federal laws, but a lot varies from state to state, just like a lot varies from country to country in the EU.

A huge number of firms treat the SSN as "private" and having knowledge of an SSN proves that you are that person. It's not what they were designed for, but good luck explaining that to the electric company and the gas company and the credit card company and the bank...

"What can you do?" With Duke Energy, the electric provider in my last apartment complex, you would have absolutely no problem registering for electric in someone else's name and having them on the hook for it if you knew their SSN.

For some reason a lot of businesses treat SSN as a secret password. Our numbers aren't supposed to be published, but they are used so often they aren't really secure.

You can do stuff like apply for lines of credit using a SSN. If you use my name and my number its presumed to be me applying for the credit.

Credit theft. People can acquire a credit card by mail or online.

That's interesting... in Spain does getting credit require an in-person appointment? Because maybe that's a simple answer to 2/3 of the identity theft in the U.S.

AFAIK yes, it always requires an in-person appointment directly or indirectly.

There are some online banks without offices, but typically they are subsidiaries of physical banks, or they have deals with them, so they will only give you credit if they have seen you at the physical bank first.

In Brazil, I can get some credit lines (usually small) by just spending more than I have on the bank, for others (a bit bigger) I'll need to enter my pin number either on a phone or an ATM, and for big credit lines, I'll have to go to the bank.

That's credit from a business you have an account with. In the US, I can often get credit from a business I have had no prior contact with with just my name and SSN. Recently, there may be multiple choice identity verification questions (pick where you used to live, what other credit accounts you have, how much their payments are, etc).

As there is a bank in every corner, I would guess yes...

The US doesn't have good standards around this for everyone, for a variety of reasons.

You can use an SSN to map to an existing credit file. From there, you establish accounts with places with poor verification practices and use them to move up the food chain.

Some states historically were very week in verification for state ID -- best case you have an audit able link between a birth certificate, lease and/or parental affidavit. Few people can be linked to a biometric. (Other than headshot photo)

SSN alone isn't thaaat bad but if you have someone's birthday and SSN you can for all intents and purposes do anything. Those two combined are basically the only proofs of identity that anything asks for. Only thing you can't do is get a passport and in some states (most now I think) you can't get a drivers license.