Observations about the addictiveness of computers, and more specifically, computer games date back at least to the mid-1970s. Addiction and addictive behavior were common among the users of the PLATO system at the University of Illinois. British e-learning academic Nicholas Rushby suggested in his 1979 book, "An Introduction to Educational Computing", that people can be addicted to computers and suffer withdrawal symptoms. The term was also used by M. Shotton in 1989 in her book "Computer Addiction". However, Shotton concludes that the 'addicts' are not truly addicted. Dependency on computers, she argues, is better understood as a challenging and exciting pastime that can also lead to a professional career in the field. Computers do not turn gregarious, extroverted people into recluses; instead, they offer introverts a source of inspiration, excitement, and intellectual stimulation. Shotton's work seriously questions the legitimacy of the claim that computers cause addiction.