I saw a lot of posts from webmaster on forums like :-
1. My bandwidth limit exceeded.
2. My site is showing bandwidth error.
3. Monthly Bandwidth Exceeded.
4. Bandwidth is out of package.
5. Ho to increase Bandwidth ?
6. How to Save Bandwidth Usage ?

Many a times Bloggers run out of their monthly usage even they dont have that much type of traffic and visitors.This might be a result of Hotlinking,it means that the images you are hosting on your site are used by other sites which accounts your bandwidth usage.
This simple tutorial of Hotlink Protection will help you in Saving Your MBT(Monthly Bandwidth Transfer.)
For Normal Users:
You can download and install the below plugin for achieving such:
Hotlink Protection Plugin
For Advanced Users:
01. Go to Your .htaccess(hypertext access) file located in public_html root and edit it using notepad and add this small code to it.(**Please take backup before editing.)
Options +FollowSymlinks
#Protect against hotlinking
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www.)?domainname.com/ [nc]
RewriteRule .*.(gif|jpg|png)$ http://domainname.com/img/stop_stealing_bandwidth.gif[nc]

Trackbacks/Pingbacks
[...] How to Save Monthly Bandwidth Limit(Hotlink Protection) [...]