I have Shop on Magento 1 and I like backend interface very much.
Some time ago I decided to go on Magento 2 and started working on local on it.
But for me Magento 2 backend interface and whole principe (console, deploying etc ) are totally nightmare comparing to Magento 1 where Backend interface is such user friendly.
So my question is - is it possible to completely secure Magento 1 from hackers?
I understand that in 2020 there will be no security patches and any upgrades for M1 but...
Anyway is there a way to completely secure your M1 website?
The bottom line is upgrade to Magento 2 for security!
However, if you opt to stick to Magento 1 for its user interface, you can have a look at https://mage-one.com/
Make sure to check the conditions and if it fulfills your requirements for security.
There might be other third party services available as well, providing security support for Magento 1!
Hope it helps.
I doubt that any one can say that a software can be made 100% secure. Definitely you can make it more secure. Only problem with staying on M1 is that in future you found some venerability Magento is not there to help. Mage-one is an initiative who may support going forward. How much they can/will can be found on their website.
To answer your questions follow the best practices, lock down your Magento means read only permissions, WAF etc and you'll be a lot safer than what you are currently.
You are like so many other merchants who really want to stick with M1 just because they are used to with it now from years.
As @Meetanshi and @Tarandeep Singh suggested about mage-one, yes they are advertising they will support after june 2020 but they will charge monthly fees for it. So if you are ok to pay then you can go ahead.
I strongly believe and urge to all current Community Members to keep take care of M1 community edition to keep it secure and compatible with latest php versions if possible and keep contributing as they are doing today for m2.
Hope the article below will guide you enough to understand what are the options available for webshop owners as Magento 1 EOL is announced.
Regarding your question on security, there are open-source communities that support Magento 1 like OpenMage. It is an affordable option. Also, Magento has recommended merchants to review their Software Lifecycle Policy to see if this includes quality fixes and security patches for their version of the platform.