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When you receive a lump sum from Social Security that includes payments for previous years, you do report the income on the return the year you receive it.
However, you have the option to make a "lump-sum election"--"you may be able to figure the taxable part of a lump-sum payment for an earlier year separately, using your income for the earlier year. You can elect this method if it lowers your taxable benefits."
In my experience, if your income is similar for 2009-2012, the lump sum election will not lower your tax....but it is worth a try to figure this out. It is a tedious process, but still worth looking into. The instructions and worksheets on how to do this are in this publication, starting on page 11... http://www.irs.gov/pub/irs-pdf/p915.pdf
Please let me know if I can assist you further.