No one seems to know, this info is based on the past shutdowns.
The section relating to Soc. Sec. is:....nebulous
Effects on Mandatory Spending Programs
Programs that are funded by laws other than annual appropriations acts—for example, some entitlement programs—
may, or may not, be affected by a funding gap. Specific circumstances appear to be significant.
For example,
although the funds needed to make payments to beneficiaries may be available automatically, pursuant to permanent appropriations,
the payments may be processed by employees who are paid with funds provided in annual appropriations acts.In such situations, the question arises whether a mandatory program can continue to function during a funding gap, if appropriations were not enacted to pay salaries of administering employees. According to the 1981 Civiletti opinion, at least some of these employees would not be subject to furlough, because authority to continue administration of a program could be inferred from Congress’s direction that benefit payments continue to be made according to an entitlement formula.
That is, obligating funds for the salaries of these personnel would be excepted from the Anti deficiency Act’s restrictions during a funding gap. However, such a determination would depend upon the absence of contrary legislative history in specific circumstances.
Nevertheless,
the experience of the Social Security Administration (SSA) during the FY1996shutdowns illustrates what might happen over a period of time in these situations. The lack of funds for some employees’ salaries, for example, may impinge eventually on the processing and payment of new entitlement claims.
SSA’s administrative history describes how 4,780 employees were allowed to be retained during the initial stages of the first shutdown.
The majority of these employees were “in direct service positions to ensure the continuance of benefits to currentl yenrolled Social Security, SSI and Black Lung beneficiaries.” Avoidance of furloughs was possible, because “appropriations were available to fund the program costs of paying benefits,
implied authority to incur obligations for the costs necessary to administer those
benefits.”
SSA furloughed its remaining 61,415 employees.
Before long, however, SSA and OMB reconsidered.
SSA had not retained staff to, among other things, respond to “telephone calls from customers needing a Social Security card to work or who needed to change the address wheret heir check should be mailed for the following month.” SSA then advised OMB that the agency would need to retain 49,715 additional employees for direct service work, including the processing of new claims for Social Security benefits. Further adjustments were made during the considerably longer second shutdown, in response to increasing difficulties in administering the agency’
entitlement programs.
http://www.scribd.com/doc/52435831/Federal-Shutdown-CRS-report