I found this to be true on my site as well as the Demo site.
A user can change your site templete as well as language by doing this:
Change uni to alt in the address line. changes site
http://demo.boonex.com/profile_info.php?ID=102689&skin=uni
Same for language from ru to en and back
http://demo.boonex.com/profile_info.php?/profile_info.php?ID=101168&lang=ru