[Atlas]

If they are using that information for a background check, they would have to inform you by law. I could see them using it for identity verification, but they should be much more transparent about that.

[thefastlane]

a recruiter shouldn't ever need any sort of 'identity verification'.

even if a recruiter is 'being transparent', there's no reason to. you should stay away from anyone saying they need to do this.

background checks, etc. are HR things that happen between when job offer is accepted and your first day of work starts.

[digler999]

I agree, and if it were background, I would expect them to need the full SSN.

[Atlas]

You can definitely do it with only the last four digits.