You should be able to remove the SSN numbers using a calculation by creating a before save calculation on the SSN attribute that sets the SSN to an empty string if the Incident.Status='Closed'. You would need to set the dependancy to Status so that the calculation fires each time the status of the Incident changes.
The following calculation should work (providing the Dependancy is set to Status)
static def GetAttributeValue(Incident):
Value = ''
Worked perfect. I added a second "if...then" statement for my Survey status. Now the analyst can resolve to a survey or an admin can close and the SSN attribute is wiped out. It's kind of neat how the attribute acts like a standard attribute in that I can assign and show and use the value in the attribute without activating the calculation. Only when I am done with the incident does it actually activate and clear my value.
I created custom Windows and a rule based on a role to allow only the approved analysts to see the SSN's value.