The practice and study of techniques for secure data communication in the presence of third parties 

Unwanted bulk messaging into email in box is known as : 

An artificial environment that is created with software and present to the user in such a way that the user accept it as a real environment 

The digital security system that uses some unique characteristic of human biology to identify authorized users:

A measurement used in comparing software and Hardware performance :

The Linux-based operating system for mobile devices developed by the Open Handset Alliance