Millions of Americans voted in the presidential elections using the simple paper ballot. Twenty-five percent embraced e-voting - but some computer experts say the machines are open to hacks.
Of the many software malfunctions and breakdowns of voting machines during Tuesday's ballot, the most famous example is a video that has gone viral via YouTube. It shows a Pennsylvania voter's choice being flipped by the machine from a vote for Barack Obama to a vote for Mitt Romney.
The glitch is unlikely to have been a deliberate software fraud – but that is not to say the machines are impossible to hack.
Professor Andrew Appel heads the Department of Computer Science at the University of Princeton in New Jersey. He suggest the problem was caused by a "miscalibration of the touchscreen hardware," or the machine not sensing the finger in the right place.
"If you have fraudulent software in the machine it is not going to indicate its presence so that the voter can see," says Appel.
There have been a number of high profile technical problems with voting machines in the past, notably in the 2000 and 2004 presidential elections.
In 2004, errors with e-voting machines in Carteret County, North Carolina, caused 4,400 votes to be lost.
But according to Professor Appel it's not just glitches that can be a problem.
He says the potential for hacking and tampering with votes is great.
"Paperless, touchscreen voting machines are not trustworthy and a hacker could easily reprogram them to produce fraudulent results," says Appel.
"You simply open up the door of the machine, unscrew the cover, pry out a memory chip, insert the new memory chip containing fraudulent software and replace the screws. And now the machine will cheat in every election in the future."
Professor Appel says "anyone with a moderate amount of computer programming experience can design fraudulent software and anyone with a screwdriver can install it."
Nor is it a particularly expensive undertaking. The memory chip would set you back around four dollars. The time it takes to install is approximately 10 minutes per machine.
There are, however, varous methods of checking voting machine accuracy, such as parallel testing - checking results from the machine against an independent set of results - or using test votes prior to the election.
Any form of tampering with voting equipment constitutes electoral fraud, the penalties for which can be severe.
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