A customer skimps on software upgrades; a malicious program storms its computers. As far as the blame game goes, this weekend’s global malware attack seems straightforward. In reality, things are more complex. A piece of "ransomware" called WannaCry blocked access to computer files in at least 150 countries on Friday, including those of the British National Health Service, Spanish telecom group Telefonica and Japanese carmaker Nissan. This could have been prevented, it turns out, had victims upgraded their old Microsoft Windows software. Instead, the U.S. maker of the operating system says they were "fighting the problems of the present with tools from the past".