Some people say that there might be duplicate content indexed for one domain by search engines. Like when someone linking to http://www.yourdomain.com/page.html and http://yourdomain.com/page.html

so what it can be done about that?

You can add this into your .htaccess file located in your domain root folder (same folder where index.php or index.html is located).


More reading:
http://www.scriptalicious.com/tools/...ect-generator/ - Nice generator
http://www.htaccessredirect.net/ - generator, see "Rewrite to www"
http://www.besthostratings.com/artic...-htaccess.html - reading
http://support.google.com/webmasters...&answer=139066 - Google about canonicalization