Scientists at a US university say they have developed a technique to hack into Indian electronic voting machines.
After connecting a home-made device to a machine, University of Michigan researchers were able to change results by sending text messages from a mobile.
Indian election officials say their machines are foolproof, and that it would be very difficult even to get hold of a machine to tamper with it.
India uses about 1.4m electronic voting machines in each general election.
A video posted on the internet by the researchers at the University of Michigan purportedly shows them connecting a home-made electronic device to one of the voting machines used in India.
Professor J Alex Halderman, who led the project, said the device allowed them to change the results on the machine by sending it messages from a mobile phone.
"We made an imitation display board that looks almost exactly like the real display in the machines," he told the BBC. "But underneath some of the components of the board, we hide a microprocessor and a Bluetooth radio."
"Our lookalike display board intercepts the vote totals that the machine is trying to display and replaces them with dishonest totals - basically whatever the bad guy wants to show up at the end of the election."
In addition, they added a small microprocessor which they say can change the votes stored in the machine between the election and the vote-counting session.
India's electronic voting machines are considered to be among the most tamperproof in the world.
There is no software to manipulate - records of candidates and votes cast are stored on purpose-built computer chips.
Paper and wax seals
India's Deputy Election Commissioner, Alok Shukla, said even getting hold of machines to tamper with would be very difficult.
"It is not just the machine, but the overall administrative safeguards which we use that make it absolutely impossible for anybody to open the machine," he told the BBC.
"Before the elections take place, the machine is set in the presence of the candidates and their representatives. These people are allowed to put their seal on the machine, and nobody can open the machine without breaking the seals."
The researchers said the paper and wax seals could be easily faked.
However, for their system to have any impact they would need to install their microchips on many voting machines, no easy task when 1,368,430 were used in the last general election in 2009.