Quick micro-blog here, but useful and important information.
Upload an .htaccess file to the wp-admin folder within your WordPress installation, then restrict access based on IP address, like so;

AuthType Basic
order deny,allow
deny from all
# whitelist home IP address
allow from 00.000.000.00
# whitelist work IP address
allow from 00.000.000.000

Replacing 00.000.000.000 with your IP address (obviously).
To find your IP on Windows, run CMD and type ipconfig
To find your IP on Mac, run Terminal and type ifconfig