Allaying all the doubts on the possibility of EVM tampering, Chief Election Commissioner Navin Chawla said on Tuesday that the machines used in India are stand-alone machines and cannot be manipulated.

"Our machines are different from the ones used in Europe and America which work on an operating system. Our machines have built-in chips and cannot communicate with anything outside. They cannot be manipulated," Chawla told reporters in Shillong after a conference of all Chief Electoral Officers of the country.

He said the machines are manufactured by two public sector units and not by private companies.

"Several courts in the country have looked into different aspects of the doubts raised and all the courts, including the apex court, have meticulously said in their judgment that the machines are completely reliable," the CEC said, adding that a three-member technical committee headed by former Madras IIT director Prof P V Indiresan had also dismissed all the doubts.

Asked whether the Commission was contemplating to revert back to ballot papers in the wake of the debate surrounding the issue, Chawla said: "Let us see. It is good to generate a healthy debate in the country."