Your privacy settings

Go to Settings › Privacy & Security. Each row decides who can see or do one thing:

• Last seen & online: Everyone, My Chats or No One.
• Profile photo: Everyone, My Chats or No One, plus a list of people to hide it from.
• Bio: Everyone, My Chats or No One.
• Messages: Everyone, or People who know my key.
• Calls: Everyone, or My Chats.

My Chats means the people you already have a conversation with.