As pointed out a while ago, Dulce also looked into the Social Security Death Index, and was heavily attacked on this discussion board of DU, for doing this.
However, this index has something to say about the official passengers of Flight 11:

There exists in the United States the Social Security Death Index. It contains death 75,163,608 Records
http://ssdi.genealogy.rootsweb.com/cgi-bin/ssdi.cgi

The SSDI does not include death records for everyone who has been issued a Social Security Number (card). Common reasons for exclusion include the following:

• The death was not reported to the Social Security Administration (SSA).
• The death occurred before the Death Master File was maintained in a computer database. About 98 percent of the deaths in this database occurred between 1962 and the present.
• The person did not participate in the Social Security program.
• Survivor death benefits were (are) being paid to dependents or spouse.
• A recent death may not be indexed yet.
• Human error. (Before you give up, read the section titled "Missing Entries in the SSDI.")

If you do not find a listing in the SSDI, it does not mean the person is still living, or that the Social Security Administration (SSA) has no records on the deceased. See "Contacting the SSA for Information" for instructions on requesting information on individuals not in the SSDI.

CREW
John Ogonowski, 52, Nothing found
First Officer Thomas McGuinness, 42 Nothing found
Barbara Arestegui, 38 Nothing found
Jeffrey Collman Nothing found
Sara Low, 28 27 Oct 1972 — 11 Sep 2001
Karen Martin 6 people with that name died in 2001. None in September.
Kathleen Nicosia Nothing found
Betty Ong, 45 ELIZABETH ONG 11 Feb 1909 — 05 May 2001
Jean Roger, 24 JOAN P ROGER 23 Aug 1940 — 20 Apr 2001
Dianne Snyder, 42 DIANNE B SNYDER 06 Jul 1945 — 25 Oct 2001
Madeline Sweeney, 35 MADELINE A SWEENEY17 Dec 1916 — 09 Dec 2001 (MARY F SWEENEY 01 Jan 1929-11 Sep 2001)