Free Theme VS Premium Theme...

What theme is secure for my wordpress@Multisite free themes or premium theme.i am so afraid to install free theme on my server because i don't have so experience about this i always thing free themes some time have some bad codes (evil) or others.But regularly i buy theme from themeforest.net .
so now my question is can i use free or premium theme for my client (Multisite) site.
Thanks Guy's :slight_smile: