In this morning's Cashin's Comments, UBS's Art Cashin addresses what worries traders these days.

A Greek default has been on everyone's minds lately. But the traders Cashin has talked to think that it's just the tip of the iceberg.

The bigger fear is what happens in the credit default swap (CDS) markets. No one knows how big it is, who the counterparties are, and, worst of all, whether the CDS contracts will actually trigger in what many would consider a default.

Here's an excerpt from Cashin's note:

As of now, most of the public discussion has centered on potential contagion among the banks as most of the Greek sovereign debit is held by the European banking community.

Traders, however, fear that the real risk is in the area of credit default swaps (CDS). They are insurance policies, individually written, that basically say - if Greece defaults, we’ll pay you what they should have.