In an attempt to pre-empt computer hackers, Microsoft is developing "virtual" PCs to scour the web for previously unseen attack code. At the software giant's Cybersecurity and Systems Management lab, based in Washington State, US, researchers are building a squad of the virtual PCs - created in software rather than hardware - to explore the darker corners of the world wide web. To any website they visit, the machines appear to be a normal home computer. But the PCs are seeking out code designed to attack a computer and will sound an alarm if any code is executed in contravention...