- An observer can typically watch the screen more easily (and less suspiciously) than the keyboard, and see which characters the mouse moves to.
- Some implementations of the on-screen keyboard may give visual feedback of the « key » clicked, e.g. by changing its colour briefly. This makes it much easier for an observer to read the data from the screen. In the worst case, the implementation may leave the focus on the most recently clicked « key » until the next virtual key is clicked, thus allowing the observer time to read each character even after the mouse starts moving to the next character.
- A user may not be able to « point and click » as fast as they could type on a keyboard, thus making it easier for the observer.
- A virtual keyboard is implemented in software and could be compromised or spoofed.