This piece in the Times and this in the Post discuss this site which "revealed" SSN's. As I understand, some USDA agency (probably Farmers Home Administration, now mostly part of Farm Service Agency) included SSN in the loan number (makes some sense because FmHA loans were to the person, covering all operations). When the data was passed to Census for its database (which subsequently passed the data to fedspending.org the SSN part of the number wasn't edited. In a way, it's a tempest in a teapot--it was discovered when a farmer got bored and googled her farm's name. When the loan data came up, of course she recognized her SSN. IMO it's unlikely a casual hacker would have deduced that 9 of the 15 digits represented the SSN (presumably the others are state and county code and check digit, but maybe not.
Whatever--it's another argument for doing away with SSN's.