A virtual keyboard is a software component that allows a user to enter characters. A virtual keyboard can usually be operated with multiple input devices, which may include a touchscreen, an actual computer keyboard and a computer mouse.
On a desktop PC, one purpose of a virtual keyboard is to provide an alternative input mechanism for users with disabilities who cannot use, or do not have access to a physical keyboard. Another major use for an on-screen keyboard is for bi- or multi-lingual users who switch frequently between different character sets or alphabets, which may be confusing over time. Although hardware keyboards are available with dual keyboard layouts (e.g. Cyrillic/Latin letters in various national layouts), the on-screen keyboard provides a handy substitute while working at different stations or on laptops which seldom come with dual layouts.
Virtual keyboards are commonly used as an on-screen input method in devices with no physical keyboard, where there is no room for one, such as a pocket computer, personal digital assistant (PDA), tablet computer or touchscreen equipped mobile phone. Text is commonly inputted either by tapping a virtual keyboard or finger-tracing.  Virtual keyboards are also used as features of emulation software for systems that have fewer buttons than a computer keyboard would have.
Virtual keyboards can be categorized by the following aspects:
- Physical keyboards with distinct keys comprising electronically changeable displays integrated in the keypads
- Virtual keyboards with touchscreen keyboard layouts or sensing areas
- Optically projected keyboard layouts or similar arrangements of "keys" or sensing areas
- Optically detected human hand and finger motions
- Virtual keyboards to allow input from a variety of input devices, such as a computer mouse, switch or other assistive technology device.
An optical virtual keyboard was invented and patented by IBM engineers in 2008. It optically detects and analyses human hand and finger motions and interprets them as operations on a physically non-existent input device like a surface having painted keys. In that way it allows to emulate unlimited types of manually operated input devices such as a mouse or keyboard. All mechanical input units can be replaced by such virtual devices, optimized for the current application and for the user's physiology maintaining speed, simplicity and unambiguity of manual data input.
Virtual keyboards may be used in some cases to reduce the risk of keystroke logging. For example, Westpac’s online banking service uses a virtual keyboard for the password entry, as does TreasuryDirect (see picture). It is more difficult for malware to monitor the display and mouse to obtain the data entered via the virtual keyboard, than it is to monitor real keystrokes. However it is possible, for example by recording screenshots at regular intervals or upon each mouse click.
The use of an on-screen keyboard on which the user "types" with mouse clicks can increase the risk of password disclosure by shoulder surfing, because:
- 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.
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