Actually it ranges from simple event spoofing (user clicked here, user dragged there) to injecting a DLL + spawning a thread under your control. Event spoofing

Actually it ranges from simple event spoofing (user clicked here, user dragged there) to injecting a DLL + spawning a thread under your control. Event spoofing is pretty limited. While having a thread under your control gives you full power as you have full access to the process' memory and can call any function you want.