In a Mac, anything downloaded from the Internet, gets tagged with a security flag, the com.apple.quarantine flag. This is really useful because it later allows the user to authorize a program to run, and avoid unwanted possibly dangerous actions to be performed.
The flag is also applied to the contents of downloaded files, so when I downloaded the WordPress installation ZIP file, and extracted it to my htdocs folder, each and every WordPress file got flagged. Really no big problem, up to when I tried to edit files from within the WordPress admin panel. Not possible…
To get rid of the quarantine flag on all WordPress files at once I used these commands:
xattr -r -d com.apple.quarantine ./*