About 1.3 million EVMs were used during the April-May Lok Sabha polls. Of these, 400,000 were new.

'Leave apart the old EVMs, the upgraded machines are not fully tamper proof,' Prasad told a gathering.

The group was accompanied by the Hyderabad-based NGO, Jana Chetana Vedika, which had earlier filed a PIL in the Supreme Court challenging the infallibility of EVMs.

The group is making another demonstration to nail the poll panel's claims next week before a technical experts team.

Prasad said mechanisms like printing a confirmation paper slip after voting, like in credit cards, would make the process more credible.