Apache DNS

I use xampp and I edit the httpd-vhosts.conf to the final of:
<VirtualHost *:80>
ServerName mysitewhonotexist.com
DocumentRoot "C:\mysite\"
</VirtualHost>
I can access My site in my computer but I ping this online, and say not exist.
Whats the problem?
Thanks, and sorry my bad English, I am Brazilian

See original post by LucRoot