How does the automatic update works in shared hosting server


My site was working just fine. Next day I see http error 500 on my site. I did not do anything between the time site is working good and the time I see the error. 

I called hosting company and they told me there was core automatic update happened to the site/files. I do not know what those updates are. I do not know why these updates break my site. How can I control it from happening it again? Please educate me on that. 


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