Prevent outsiders from being able to inject malicious code

Hello, I researched how to disable Script Injections and I found the following code, however, it doesn’t say which file to place it into. Does anyone know where to put the following snippet?

It says: “… use this snippet to prevent outsiders from being able to inject malicious code into your existing PHP files:”

Options +FollowSymLinks
RewriteEngine On
RewriteCond %{QUERY_STRING} (<|%3C).*script.*(>|%3E) [NC,OR]
RewriteCond %{QUERY_STRING} GLOBALS(=|[|%[0-9A-Z]{0,2}) [OR]
RewriteCond %{QUERY_STRING} _REQUEST(=|[|%[0-9A-Z]{0,2})
RewriteRule ^(.*)$ index.php [F,L]