Type in your terminal:
$ find /etc -type f -printf '%TY-%Tm-%Td %TT %p\n' | sort -r .
If you want to see directory files, type in your terminal:
$ find /etc -printf '%TY-%Tm-%Td %TT %p\n' | sort -r .
Unfamiliar modifications in the last 7-30 days may be suspicious.