Security issue related to wp-tmp.php

Hi,

I have installed ithemes security plugin on my website. I have even secured it with all best possible configuration which is suggested by ithemes plugin at time of installation.

File change scan is also active.

but today i got mail from my hosting provider that my site my web place has virus file name wp-tmp.php and due to this they have stop my web ports.

I want to know how can my web place be infected when i have ithemes plugin and how such file got placed into my web folder. do i have to do any specific setting then please let me know.