Hopefully he's not as clever as the hacker that hacked this guy's accounts.
http://www.wired.com/gadgetlab/2012/08/apple-amazon-mat-honan-hacking/
However, that story has nothing to do with the last 4 digits of the SSN.
The account mentioned, was reset using the billing address and the last four digits of a credit card on file. The moral of that story, shred all your important papers.
I agree, just the last 4 digits of your SSN, by itself, is probably harmless. Unless the hacker can also get hold of your account number or credit card number or a fake ID as well.
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