> As far as I know, the only organisation that you're required to give it to is the tax office itself. Interestingly, by virtue of this number being so 'secreti

> As far as I know, the only organisation that you're required to give it to is the tax office itself. Interestingly, by virtue of this number being so 'secretive' it really is usable as an identifier only to the tax office. Amusingly, the IRS doesn't actually ask you for your SSN as your identifier when you need to do basic things (like replace your social security card). I know of someone who was prepared to give it to them, and the agent actually scolded him, "Your social security number isn't an identifier".