The only physical proof of its' existence is the information that is transmitted through the computer. We depend on a network of computers to bring our virtual world together. It is real because we experience bits of it through a screen. Virtuality literally means existing in the mind. Our minds make the Internet a reality.
Minds interact through organized content.
That is, our mind communicates with other minds and the content of the exchange is organized by topic and by attitudes towards the topic. In this sense cyberspace is an interconnected and organized like the mind. Cyberspace is a collaboration of infinite minds, which behave according to the organization of thought processes such as communication or responses. The mind can live multilocally. Perhaps someday it can attain its own independent consciousness.