On QQ International you have full control on how you want to be found by other contacts, and whether to appear or be hidden to the wider QQ userbase.
QQ International for Android and iOS
First tap on the Settings tab in the lower navigation bar and then “Security and Privacy”:
From this menu you can control every single aspect of your visibility to other users who still haven’t added you to their contact list.
QQ International for Windows
Go to Settings from the main panel:
Then go to Privacy and Visibility: