How can I make my XAMPP installation more secure?

In the default installation, XAMPP has no passwords set and it is not recommended to run XAMPP with this configuration accessible by others (e. g. on the Internet).
Simply type the following command (as root) to start a simple security check:

/opt/lampp/lampp security
Now you should see the following dialog on your screen (user input is highlighted):

XAMPP: Quick security check...
XAMPP: Your XAMPP pages are NOT secured by a password.
XAMPP: Do you want to set a password? [yes] yes (1)
XAMPP: Password: ******
XAMPP: Password (again): ******
XAMPP: Password protection active. Please use 'lampp' as user name!
XAMPP: MySQL is accessable via network.
XAMPP: Normaly that's not recommended. Do you want me to turn it off? [yes] yes
XAMPP: Turned off.
XAMPP: Stopping MySQL...
XAMPP: Starting MySQL...
XAMPP: The MySQL/phpMyAdmin user pma has no password set!!!
XAMPP: Do you want to set a password? [yes] yes
XAMPP: Password: ******
XAMPP: Password (again): ******
XAMPP: Setting new MySQL pma password.
XAMPP: Setting phpMyAdmin's pma password to the new one.
XAMPP: MySQL has no root passwort set!!!
XAMPP: Do you want to set a password? [yes] yes
XAMPP: Write the passworde somewhere down to make sure you won't forget it!!!
XAMPP: Password: ******
XAMPP: Password (again): ******
XAMPP: Setting new MySQL root password.
XAMPP: Setting phpMyAdmin's root password to the new one.
XAMPP: The FTP password for user 'nobody' is still set to 'lampp'.
XAMPP: Do you want to change the password? [yes] yes
XAMPP: Password: ******
XAMPP: Password (again): ******
XAMPP: Reload ProFTPD...
XAMPP: Done.


(1) Setting a password will protect the XAMPP demo pages (http://localhost/xampp/) using this password. The user name is 'lampp'!

After calling this command your XAMPP installation should be "secure".