Well, you can read the source code. But if you're downloading Omen from WoWAce.com, then it's in a form that can't exploit your computer, as I said above.

Addons are very heavily sandboxed, so it's unlikely to be that. Basically an addon can do things within the game, or save its data to a file and that's it.

The only way an addon could do more is if it wasn't just an addon - such things typically install from executable binaries rather than zip files. Unless you *absolutely* trus the source (such as WoWAceUpdater), steer clear from these