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Let's think about this: 

I just cleaned up some old Joomla websites where owners did not realize how important to keep Joomla! and its extensions up-to-date.

Starting with Joomla 3.5, anonymous statistics are gathered : 22% of Joomla 3.5 website updated to version 3.9. Nobody knows how many are still working with Joomla prior 3.5, but just take a look at the number of messages on Joomla forum, taking about old versions, I let you image it. Have a look at Joomla Usage Statistics

On forum.joomla.org, sozzled gives a wake-up call for people using old versions of Joomla.

You don't know how to update your website, have a look at our maintenance plans.

I did not convince you, just have a look at Sucuri's article : What Hackers Do after Gaining Access to a Website.

You are still working with old Joomla version, and you still don't understand how hackers entered and messed up everything : since may 2017, Fortinet gives to everyone old website's keys to enter and play...