One of the many ways you could lose money on Lehman (owning its stock, being a derivatives counterparty, using it as a prime broker, or just having any involvement whatsoever in the global financial system) was by investing in its principal protected notes, structured notes that are typically zero-coupon and at maturity return the greater of (1) par or (2) some higher amount based on returns on some other security or index (heres one Barclays issued last Friday ). These are a way for banks to get cheap funding by packaging an unsecured debt security with an equity/credit/commodity/whatever derivative and selling it to customers who dont have ISDAs or otherwise arent down with OTC derivatives. Theyre called principal protected because even if the linked index goes down, you still get all your money back (albeit at zero yield). But that only happens if the issuer doesnt go bankrupt if they go bankrupt, youre hosed just like other noteholders.

Which, duh, or so we thought. The notes after all said that they were Lehmans unsecured obligations and that an investment in the Notes will be subject to the credit risk of Lehman Brothers Holdings Inc, and the actual and perceived creditworthiness of Lehman Brothers Holdings Inc. may affect the market value of the Notes. But that wasnt enough for these plaintiffs, or for the judge, who is going to let the structured notes claims go to trial:

While these statements would have made the nature of these securities clear to a careful and intelligent reader, the principal protection statements were displayed more prominently and frequently than the warnings. The first line of the each pricing supplement submitted with the defendants’ motion states 100% principal protection in large letters. The first page lists the Features of each investment, which include 100% principal protection if held to maturity and [a]t maturity, you will receive a cash payment equal to at least 100% of your principal. Each mentions 100% principal protection at least four times on the first page. By contrast, the risk that investors could lose their principal if Lehman went bankrupt is not mentioned on that page at all.

So the advice to structured notes desks is (1) put everything on the first page and (2) dont assume that your customers are careful and intelligent readers.

How can we put this gently? We suspect that part of the appeal of issuing structured notes is that not every single one of your buyers is careful and intelligent. And we suspect that banks were not exactly sad that retail customers thought 100% principal protected really did mean that you couldnt lose money even if the issuer went bankrupt. Thats probably going to be harder to get away with after todays ruling.