Core File Changes

For some reason I am getting a lot of Core Files Changes happening. I only know this because I am using Wordfence Security and it keeps alerting me to the changes.

I am assuming that at some point some malicious code has been installed somewhere, the site has been hacked a couple of times in the past which is now why I am using Wordfence.

Wordfence has removed some malicious files for me today.

Any thoughts please on how I can secure the site better to stop core files being changed ?