Restricting the access to the critical Joomla directories such as “administrator” by IP address is a good security measure. This way you can allow access to your Joomla backend only from your own IP address.

In order to implement such a restriction you have to add the following lines in your .htaccess file residing in the directory you wish to protect:

Order Deny,Allow
Deny from all
Allow from 123.123.123.123

where the sample IP address 123.123.123.123 has to be replaced with your own IP.

You can find what your IP is at http://whatismyip.org