Nearly 3 year old hurting baby

[Lovelilies]

Help!
My nearly 3 yo DS has taken to hurting his baby sister (6m)
He's just now bitten her on the finger. We were all on the sofa and I thought he was kissing her hand and he looked right at me and bit her! He's on the bottom stair now as I type.
Recently he's been smacking her on the head, and little punches, kicks. He makes no effort to hide this. He gets plenty of 1-1 attention, but he also winds his big sister up poking and hitting her.
I tell him off every time and have been using the step as a last resort (used effectively with DD1 but she learned quickly and I've since read up a bit about how it can be damaging to 'abandon' little ones emotionally when they're obviously in need of connection. However, I need to stop this behaviour immediately for my DDs sakes!
Please help me!!

Anyone?

I would say he's enjoying your reaction, to him it may seem rather comical! I've caught my 3.5 year old dd1 trying to "operate" on her baby sister (10 months) but she really means no harm. If possible, distraction can work, praising good interaction (like be more comical if he does something nice for baby/gets a reward). I really don't think he's trying to hurt the baby, more trying to get a reaction from you. Just a firm "no" that's not funny/clever/kind. Maybe buy some stickers with his favourite characters on and every time he does something helpful, he gets one! I hope this helps, it's late and I'm tired so hopefully not rambling! Good luck!