Thomson ReutersYou might have heard that traders at the biggest US investment banks have been curtailed. So how is it that a 34-year-old Goldman Sachs trader made a $100 million profit in just a matter of months? Justin Baer at The Wall Street Journal lifted the lid on the trader, Tom Malafronte, in a great story published Wednesday. Baer reports that Malafronte, who works on the high-yield desk, bought billions in dollars in junk bonds in January from clients anxious to sell, and then sold them later for a higher price. You might be asking, isn't that kind of thing supposed to be been banned by restrictions like the Volcker rule? It is reasonable to ask that question.