The internet is composed of many web sites with most written in PHP, some in python and many other sub languages which are based on other proprietary formats.
The heavy use of PHP necessitates the issuance of frequent updates which addresses security issues and flaws that prevents hackers from getting access or control of vulnerable implementations of systems using PHP in Windows. Windows Being the most targeted Operating System makes it very vulnerable but thanks to the open nature of the web, any security flaws that are found are immediately found and announced getting the community on the hunt for an immediate solution.
Older systems had big companies finding flaws and solving them without users knowing of such cases till they are greeted by updates for the support websites or get news of a problem with security through the news. Gone are those days and in with the community who discusses and solves problems jointly maximizing the reach of the internet with several people working to solve the problem it becomes cheaper and faster to solve these security issues without much financial needs of a corporation.