Maybe you didn't know that the rogue trader at UBS AG who lost $2.3 billion last year was trading exchange-traded funds (ETFs)... or that Jerome Kerviel, another rogue trader at Societe Generale who lost $7.2 billion in 2008, was trading ETFs. Maybe you didn't know that ETF trading accounts for 35% to 40% of all exchange volume, according to Morningstar Inc. Well, what you don't know can hurt your investments...