My one year old is hitting!

My daughter literally just turned one a few weeks ago. I swear it started the day after her birthday. She will smack you or scratch your face. She will hit when she is mad at you and sometimes just because. We hold her hands down and tell her no hitting, then will smack you again as soon as you let go. Today she hit me with one hand, I grabbed her hand and told her no hitting. She literally cocked her other hand back and was getting ready to punch me with the other! I looked at her firmly in the eyes and she put her hand down. She knows it's wrong. So wtf! How can I possibly get her to stop?