Strange redirct if wrong url is entered

[Menace]

Hello all,

no that I am nearly done with my first VM shop I noticed a strange behaviour while testing the site.

Joomla and VM SEO are active. Everything works fine when browsing through the menus and items. But if I type a nonexisting url into the browser like 'mynewsite.com/qwerty' I am redirected to 'mynewsite.com/index.php?option=com_virtuemart' which gives me a site with partly broken template, showing nothing but sites background and the topten products I use on the Homesite.

What will I have to do to permanently redirect to homesite instead?

Using Joomla 2.5.4 with VM 2.0.12f