Security software firms worked with international law enforcement agencies, the FBI and the Georgia Tech Information Security Center to neutralize and eventually arrest three criminals who allegedly masterminded a massive botnet scam that ensnared more than 13 million PCs. The suspects, who officials say called themselves the “Nightmare Days Team” and dubbed their botnet project “Mariposa,” were arrested at their Basque Country residence by Spanish authorities last month. The arrests came after a year-long investigation by local law enforcement agencies and security software vendors Panda Security, which is headquartered in Bilbao, Spain, and Defence Intelligence of Ottawa, Ontario.