Oh, uh...can you uninstall it in Control Panel? Or maybe run a virus scan? I dunno what to tell you about Firefox, or Chrome, then. I'll search for how to disable the warnings in Opera.
EDIT: Go to Settings > Preferences > Advanced > Security and disable the fraud and malware warnings, if you don't want them to show up any more. You may need to be a little more careful in the future, though, as it seems impossible to tell it this specific site is safe.