On Wednesday Spanish authorities announced the arrest of three alleged ringleaders behind the Mariposa botnet. Mariposa is possibly the largest botnet yet discovered and consisted of an estimated 12.7 million computers.
The extent of the virus-infection is staggering: more than 190 countries, over half of the Fortune 1,000 large enterprises and at least 40 major banks were affected. Online banking credentials, credit cards and passwords were targeted by the group running the botnet. More details here.