Yesterday it was revealed that five of the world's biggest banks - including HSBC and RBS - were fined £2 billion for manipulating foreign exchange markets.
Here, we take a look at how they did it.
Sharing sensitive information
Traders from different banks shared information about client activity in online chat rooms, using code names to identify the clients.
This helped them work out their trading strategies as they attempted to ensure that the rate at which the bank had agreed to sell a particular currency to its clients was higher than the average rate it had bought that currency for in the market. If successful, the bank would make a profit.
Their focus was on the 4pm fix, the daily minute in the London trading day when major exchange rates are set.
A typical fix would see the bank with the largest amount of money to trade that day "build" on the sum by working with other banks to take on their orders - sometimes totalling hundreds of millions of pounds.
It meant the bank could have a "huge" share - up to half - of all money traded on the market that day, while up to 40 other market participants made up the other half.
It gave the bank greater influence to manipulate the rate, which saw all banks involved benefit from the fix.
Therese Chambers, the Financial Conduct Authority's head of wholesale enforcement, compared the impact of the method to a dozen people throwing pebbles into a pond while one person throws a rock.
She said: "Obviously banks are entitled to manage their risks but what is completely unacceptable here is that they are not seeking to manage their risks, they are seeking to directly manipulate the fixed prices and taking whatever steps they think will help them to achieve that goal - that's about as far from legitimate trading as you can possibly get.
"They are not coordinating for their customers, they are coordinating for their own bottom line."
Fixing the rate to move lower
In the case of Royal Bank of Scotland, the Financial Conduct Authority highlighted an example where the bank stood to benefit if it was able to move the fix rate lower.
The chances of successfully manipulating the rate in this manner would be improved if RBS and other firms adopted trading strategies based on the information they shared with each other about their net orders.
In the period between 3.22pm and 3.54pm, traders at four different firms including RBS inappropriately disclosed to each other via a chat room details of their net orders in respect of the forthcoming 4pm fix.
Through a series of trades conducted with other market participants, RBS "built" the volume of currency that it needed to sell at the fix to £399 million, well above that necessary to manage the risk associated with client orders.
In the 60-second fix window, RBS sold £182 million, which accounted for more than 32% of the sales in dollar exchange on the Reuters platform as RBS and another firm accounted for 41% of business.
During this period, the exchange rate fell from 1.6233 to 1.6213 and RBS's trading in the dollar fix generated a profit of 615,000 US dollars (£389,000) .
The trading was discussed by the participants in the chat rooms subsequent to the fix, with references to "I don my hat", "welld one (sic) lads", "what a job", "bravo" and "(RBS) is god".
While consumers were not directly affected by the organised rigging of rates, Ms Chambers said the reputation and integrity of the largely London-based trading had been damaged.
Asked who the victim of the fixing was, she said: "The market place. The reputation of the market place, the integrity of the market place. London takes 40% of the FX market, that's important to this county.
"It's important that it is seen as clean."
In one example, a profit of 162,000 US dollars (£102,000) was made by HSBC in just minutes of trading.
She said it was clear from the examples of messages shared in online chat rooms that fixing was "not a novel practice".
Messages swapped included one trader boasting of "the best fix of my UBS career" while a trader from another bank replied: "Challenge?"
Others told each other "We f****** killed it", "well done lads" and "every time" after manipulating the market together.
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