If someone were to break in your room, they would probably learn less about you than if they hacked you on the internet. Our efforts towards security have to be as intensive online, as they are offline.  
An extremely popular Content Management System, Drupal is on top of the list for many. 
Very importantly, Drupal has a dedicated team to make sure that the Drupal core is largely free of loopholes or vulnerabilities that may compromise website security. 

Drupal powers more than 7,00,000 sites across the internet, which increases the chance of a specific site owner being vulnerable to cyber attacks. 
Although all third-party modules are heavily vetted, a little extra security is always a good idea.