Breaking News: Cyberattacks have now been reported in 12 countries, apparently using a security loophole that emerged from a leak of N.S.A. documents

An extensive cyberattack struck computers across a wide swath of Europe and Asia on Friday, and strained the public health system in Britain.

The attack involved ransomware, a kind of malware that encrypts data and locks out the user. According to security experts, it exploited a vulnerability that was discovered and developed by the National Security Agency.

Read more »