For two years, SpyEye was the world's most destructive piece of malware targeting banks and financial institutions, infecting more than 50 million PCs and causing estimated damage of $1 billion. The malware, created by a young Russian hacker who liked to brag of its malevolence, was secretly installed on victims' computers, spread via spam emails and malicious websites, and worked by silently stealing the banking and credit card details of millions of people.