What is PHP, and how bad is the computer language flaw causing website shutdowns globally?

A newly disclosed PHP flaw has prompted governments and businesses to take websites offline while they install security patches. The vulnerabilities could let attackers corrupt memory and reach a server’s files or database, putting a widely used part of internet infrastructure at risk.

PHP is used by an estimated 70% of websites, including sites built with WordPress and Drupal; Wikipedia and Facebook are among the services identified as affected. The PHP Foundation says the flaws involve memory management and error handling, and patches are available. The disclosure was brought forward after the vulnerabilities began circulating online, and security firms report exploitation at scale.