This is something that happens a lot and it is very dirty,  as you probably know each site is hosted on a certain IP address.  Sometimes a domain is hosted by a single IP address and the IP address defaults to this very same domain.

This means that if someone buys domain abcd.com and enters your IP address (the one of your website) as the A record, your content will show up on their domain as if it was their own.

There is an easy way to prevent this by using .htaccess, these 2 lines of code simply tell Apache that if your content is being accessed by anything other than yourrealdomain.com to redirect to "yourrealdomain.com":


RewriteCond %{HTTP_HOST} !^yourrealdomain.com
RewriteRule ^(.*)   http://yourrealdomain.com/$1   [R=permanent,L]

This will prevent sites from hijacking your content.   I know people say Google can detect duplicate content and which site was the original one, but I don't believe this.  A domain that hijacked one of my sites started getting our content indexed under the domain name they used to hijack my content.

This is something that you should put in the .htaccess of every site you have to prevent this, it also has the benefit of eliminating difference links pointing to the www. version of your site, this forces everything to your root domain.