The most high-profile case has been Lehman principal-protected notes, which were sold as high-yield bonds.

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Another batch of can't-lose stock investments came in 1992, when commercial banks sold equity-linked, principal-protected certificates of deposit.

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There are two more twists to principal-protected notes that investors need to understand: First, they're unsecured obligations of the banks that issue them.

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Some states offer prepaid tuition plans with guaranteed or principal-protected options.

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Unlike principal-protected notes, these offer no protection if stocks sink.

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This note has a term of six years, is principal-protected, and the return is linked to the value of a global index basket made up of the Dow, the Nikkei, and the Euro Stoxx 50.

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The trust can distribute income to beneficiaries (who will pay income tax on these distributions of income), but principal is preserved, asset-protected and grows tax-free.

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Finally, you could buy Treasury Inflation-Protected Securities (TIPS) whose principal and interest payments adjust with inflation.

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Combining derivatives with high-yield notes had gotten untold numbers of investors into trouble, especially those who invested in Lehman principal protected notes, which went belly up and left investors holding the bag.

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