The recent difficulties faced by Greece (and some other eurozone states) in rolling over their national debt has let some to blame hedge fund involvement in the market for credit default swaps. These contracts can be used to insure bondholders against the risk of default, but when purchased naked (without holding the underlying bonds), they can serve as highly leveraged speculative bets on a rise in the cost of borrowing faced by the sovereign states.
A cogent case for prohibiting the use of credit default swaps to make directional bets has been made recently by Wolfgang Münchau in the Financial Times:
I generally do not like to propose bans. But I cannot understand why we are still allowing the trade in credit default swaps without ownership of the underlying securities. Especially in the eurozone, currently subject to a series of speculative attacks, a generalised ban on so-called naked CDSs should be a no-brainer...
A naked CDS purchase means that you take out insurance on bonds without actually owning them. It is a purely speculative gamble. There is not one social or economic benefit. Even hardened speculators agree on this point. Especially because naked CDSs constitute a large part of all CDS transactions, the case for banning them is about as a strong as that for banning bank robberies.
http://rajivsethi.blogspot.com/2010/03/defenders-and-demonizers-of-credit.html