Safe to install NIS on unscanned system?

Hello,

 

This is my first post but I've tried to find an answer to this question but so far no luck

 

Although I have a hardware firewall attached to my system I would like to add NIS. However, I have to download NIS and install it direct before any scan takes place. Does this pose a problem? Can the installation be interfered with by a Trojan or virus or whatnot? Or does it matter? I suspect my system is clean, but you never know. Any advice?

 

Many thanks.