Why I can't remove Security Anivirus?

I download this Security Anitvirus but then when I want to uninstall it I can't find it anywhere in my computer to uninstall. I can only find it on my menu so I delete it.However when I turn on my computer again it reappear, I try finding it in hidden files but still can't see it. Also it kinda of giving me viruses. So how can I Uninstall Permenently?