Two vulnerabilities found in the programming language PHP put enormous swaths of the internet in danger. By some accounts, up to 70 percent of websites use PHP in some capacity.

It powers Wikipedia, WordPress, Drupal, and a host of other popular sites and platforms, including DeviantArt and 4Chan, which were temporarily shut down after the vulnerabilities were disclosed. Even governments weren’t immune.

But it’s not as simple as updating a few servers. The vulnerability exists in every version of PHP dating back roughly 20 years, many of which are no longer supported.