What is the most vicious bird?

The most vicious of birds is probably the cassowary, which has a forceful kick that will and has proven to result in injuries and death in many cases. If you ask of what is the most vicious bird to walk the earth, I'd say it's a terror bird (Scientific genus: Titanis). This bird could smash the skull and destroy the brain of a full-grown horse. However, it became extinct because it couldn't compete with it's neighbor's the saber-tooth, and the wolf (I forgot the wolf's name).