I have been using Viart Shop Standard for many months but, suddenly, the "Powered by Viart Shop" logo and link appeared in the bottom right corner of the page.
As a registered version this should not be so - how do I remove this?

Hello,
 
"Powered by Viart Shop" logo is not connected with the license.
 
From what you have described, it seems like you had changed your footer.html file somehow.
In order to remove the link 'Powered by ViArt' (in the footer) you are to delete the appropriate link from the 'footer.html' file in the .templates/user folder:
<div class="footerImg"><a title="ViArt - PHP Shopping Cart" href="http://www.viart.com"><img alt="ViArt - PHP Shopping Cart" src="images/tr.gif"></a></div>
</div>
</center>
Save the file and the link 'powered by viart' will be removed from your site.
 
Regards,
ViArt Support Team

Also, if you change your domain name the license.php file in /includes/ becomes invalid. As soon as something is broken with this file the footer link + logo appears again.
 
You might want to try to re-download a license.php from www.viart.com/activation

I think Denis is right.
 
My footer had to be changed recently because Viart advised me that the javascript code it contained was causing problems in the checkout.
 
Logo removed, thanks.