Voting machines pose "serious risks" to US security, hackers are warning.
A report outlines major flaws in voting hardware, weeks before US mid-term elections.
One ballot machine, used in 23 US states, carries a cybersecurity flaw that was reported over a decade ago, the hackers claim.
Other machines tested include the AccuVote TSx, currently used by 18 US states. The system includes a smart card reader for users to cast votes, which the report says can be easily disconnected to "disrupt the election" process.
Attendees of the conference were also able to reprogramme voting smart cards wirelessly, using mobile phones.
On Tuesday, Republican Senator James Lankford said an election security bill, known as the Secure Elections Act, would not be passed by Congress ahead of the mid-term elections in November.
Earlier this year, an amendment for $250m (£192m) to increase spending on election security measures was blocked by Republican senators.