Four of the world's biggest banks—Citigroup, JPMorgan Chase, Barclays and Royal Bank of Scotland—have pleaded guilty to a scheme that was intended to rig the value of world currencies for the benefit of traders in each, according to the New York Times. A fifth bank, UBS, was also involved, though this has instead led to the government to rescind a previous agreement not to prosecute the bank on separate charges of rate rigging, said the Times, leading the Swiss bank to plead guilty to that. Collectively, they have agreed to pay about $5.6 billion in penalties, on top of $4.25 billion that some of them had already agreed to pay in November, said the Times. 

Through entering the guilty plea, the banks have admitted to, from between 2007 and 2013, having near daily conversations with each other on manipulating the global currency market, usually in a private chat room called, appropriately enough, "The Cartel" or "The Mafia," according to NPR. 

To do so, said the New York Times, a trader at one bank would built a large position in a particular currency and then unload it all at once. Traders at other banks, coordinating through the chat room, would treat it like a legitimate trade and, essentially, play along. Further, the banks also misled their own clients about the price of the different currencies, said the Times, often at a much higher price than it actually was. 

While ordinarily, after a felony plea such as this, the banks' ability to operate in the U.S. would be considered all but dead, the Securities and Exchange Commission (SEC) has issued waivers for each of them allowing them to continue operations, despite technically being criminals, according to Bloomberg. Investors seemed to understand that the convictions were largely symbolic, as stock prices for the banks barely budged in response to the news.