This is a story about the SoakSoak malware campaign that proved that you can’t underestimate impact of security issues in popular premium software.
These days, the majority of popular content management systems are 100% free: WordPress, Magento, Joomla, Drupal, etc. Moreover, most CMS extensions are also free. In fact, modern webmasters can build any type of site entirely through free software. Most popular software has thousands — or even millions — of installations.