An investigation into conduct by traders at some of the world’s biggest banks hit a major milestone on Wednesday when six of them agreed to pay a total of more than $4 billion to regulators from three different countries to settle allegations that they had tried to manipulate the foreign currency markets.

While the outcome is bad news for the banks involved—Citigroup Inc., HSBC Holdings plc, The Royal Bank of Scotland plc, Bank of America, UBS AG and JPMorgan Chase & Co.—there are some good lessons for in-house compliance professionals.