Strange file on my website dismask.php

[xnitrorc]

Hi guys i need help with my website today checking my stats in google webmaster i spoted people finding my website for strange search terms not relevant to my site in any way shape or form.

there is a strange php file on my site showing in google search results the file is dismask.php i cannot find this in ftp to remove it.

If you go to google and type any word followed by dismask.php my site shows up an example:

www.xnitrorc.co.uk/dismask.php?o=milk-and-more (search google for strange file dismask.php)

www.xnitrorc.co.uk/dismask.php?o=bachmann (search google for flowers dismask.php)

When you click those links my site returns the error 404 so there are no actual pages but this file is annoying me as i have just spent a very long time rebuilding the site from scratch migrating from joomla to prestashop and dont fancy doing it again.

has my site been hacked ?

anyone help me with this strange file ?

The 1st 79 top search results in google webmaster are for nothing to do with my kewords at all!!