"Libor rigging"

U.S. and British authorities on Wednesday (25th September 2013)fined ICAP, the world's biggest interdealer broker, $87 million and criminally charged three former employees for their role in the Libor benchmark rate rigging scandal.

Read the whole article http://www.reuters.com/article/2013/09/25/us-icap-libor-idUSBRE98O0BX20130925   and answer the questions below.

1. What is Libor and why was it "rigged"?
2. Who will face criminal action?
3. Which other banks have been affected already?
4. How do you think this could have been prevented?

Answers in the comments please.