The Wall Street owned insurer Customer Asset Protection Company, known as Capco, may not be an off-shore company. But it sure operates like one of those Cayman Island based tax shelters president Barack Obama has targeted.

Capco is the mysterious company owned by WallStreet giants like Morgan Stanley and Goldman Sachs, banks like JPMorgan Chase and Wells Fargo, smaller brokerage firms, and Fidelity, the mutual fund giant. Years ago Capco moved from New York to Vermont, where state law enables it to operate without disclosing much about its finances.

It’s official address is 100 Bank Street, Suite 610, in Burlington, Vermont. But if you go there, you won’t find an office marked with the name Capco. Instead, you’ll find an office marked Marsh Captive Solutions, which is a division of Marsh & McClennen that administers captive insurance companies. A total of 185 business are run out of Suite 610.

This brings to mind the story Obama used to tell on the campaign trail about “the outrage of a building in the Cayman Islands that had over 12,000 business — businesses claim this building as their headquarters. And I’ve said before, either this is the largest building in the world or the largest tax scam in the world.”

So how big is Suite 610? We suspect it’s a small office with a bunch of secretary types and filing cabinets.  The reason it houses so many companies is that these captive insurance companies are registered in Vermont to avoid tighter regulations in other states.

For those of you who missed it, today Capco was dragged out of the shadows by New York Times reporter Zach Kouwe. The company was formed to insure customer accounts above the $550,000 of SIPIC insurance. The idea was that customers didn’t need to worry about the insolvency of their broker because Capco was insuring it. But now Capco appears to be massively insolvent, facing a possible $11 billion in claims from the collapse of Lehman Brothers with only about $150 million with which to meet them. New York State regulators are worried, and the Wall Street owners could wind up having to pay the bill.