[CLBS] Social Security lump sum payment for missed months

[Drake Mesenbrink]

A client has been disabled for about 2 years.  He applied for social
security disability.  It took Social Security about a year to grant his
application.  Social Security then made a lump sum payment for the months
during which Social Security was working on the application, and he now
receives monthly payments as well.

Since the lump sum payment was Social Security and was for a reason of
disability.  Is it still exempt? 603(3) and 604(1)(a)

Thank you.