Barclays Bank has been fined a total of $450,000,000 (approx) by regulators for "fixing" the LIBOR rate. LIBOR used to be an obscure statistic but these days everyone knows it underpins all unsecured lending, and even spills over into secured loans such as mortgages since banks often borrow unsecured to lend secured.
It seems Barclays has been pushing LIBOR up or down according their needs on the day. Sometimes they felt they should under-report their borrowing costs to make themselves look a safer prospect, able to borrow cheaply, and other times they pushed it up in order to win a market "bet". (And do not forget: for every winner of a bet there is also a loser - a loser who may now wish to revisit the bets in question.)
Their traders openly cooked up LIBOR in emails around the bank. There does not seem to have been much covertness or shame inside the bank. If someone needed LIBOR rigged they just asked the right guy and it happened.
There have been suggestions that LIBOR has been rigged before. Back in 2008 a small number of American banks were investigated for under-reporting their LIBOR to make themselves look healthier than they were. To-date nothing has come of this.
However, just misreporting your borrowing costs does not make a big shift in the LIBOR rate. The reason for this is that to calculate the LIBOR the four highest rates and four lowest rates are disregarded, and the average taken of the rest. If a bank made an extreme report it would be disregarded.
Unless of course, it gets together with four or more other, like-minded, banks and they agree to push the rate up or down. Then they can really have a significant impact. And the more banks joining the conspiracy the bigger the bang.
The regulators, by the way, are still looking at more than twenty other banks. Barclays has merely copped an early plea in order to get off lightly. This story will run and run.