Remove System Account access to sharepoint Site collection

Question

Hi,

 

Actually we have some confidential data in site collection and we don't want to allow any user to access it. For that I have added one user as a site collection administrator and removed all users. Except that user there is no other users are having any permissions to this site collection. And i didn't see any permissions for Farm administrator for this site collection. But i can log into the site with Farm administrator as a "System Account".

 

Here i want to know how can we remove access for Farm administrator to the site due to some confidential data. 

Any help would be greatly appreciated.

 

Regards 

Saya