In a sign of increasing anxiety over the use of electronic voting machines, the Republican National Committee this week alleged problems with e-voting machines in six states that use them for early voting.

John Phillippe, general counsel of the RNC, contended in a letter to the secretaries of state in Nevada, Ohio, Kansas, North Carolina, Missouri and Colorado that voting machine errors caused some early votes cast for Gov. Mitt Romney to be credited to President Barack Obama.

Phillippe said in the letter that the RNC learned about the alleged voting machine errors from media and citizen reports.

"I understand that, in a significant number of cases, voting machines in your states have populated a vote for Barack Obama when a voter cast his or her ballot for Mitt Romney," Phillippe wrote. "I further understand that the causes of this problem are varied, and include miscalibration and hyper-sensitivity of the machines."

Phillippe asked that election officials in the six states re-calibrate the voting machines on election day or one day before the elections. It also asks that additional technicians be available on Election Day in case of "increased calibration problems."

Phillippe also called on election officials to ensure that voters are reminded to "double-check that the voting machine properly recorded their vote before final submission."

The RNC letter evoked an angry response from a Nevada Secretary of State Ross Miller, who called the RNC claims "irresponsible" and "unfortunate," and said that they are based on rumor, hearsay and unconfirmed media reports.

"Unfortunately your letter fails to provide any direct evidence that any particular voter in Nevada experienced any 'errors' with their voting machines or any details which could be used to open an investigation," Miller wrote in a letter to RNC officials.

Miller said the RNC letter didn't identity any affected voters whose votes were allegedly miscast, or any polling place where the errors allegedly occurred.

So far, he said, the state has not received a single complaint from early voters regarding their use of electronic voting machines.

Miller contended that it's "technically impossible" to pre-program e-voting machines in Nevada to vote for a specific candidate. The machines are tested by officials in each of the state's 17 counties, he noted.

"While it is possible for a voter to inadvertently select a candidate, it is not possible for the machine to automatically select a candidate," Miller wrote.

Miller added that his office, along with the FBI and Nevada state attorney general's office, had investigated similar complaints in 2010. That probe concluded that any claims that Nevada's electronic voting machines malfunctioned or were pre-programmed lacked merit.

Gary Bartlett, executive director of North Carolina's State Board of Elections said the "rumors and hysteria" surrounding vote switching has centered on some incidents in the state's Guildford County.

Since early voting began on Oct. 18, voters reported 24 problems with the touchscreen Direct Recording Electronic (DRE) voting systems used in the county. In each of those incidents, the voters were able to review and change their votes before casting a ballot, Bartlett said in a letter sent Friday to the RNC.

There were a "handful" of problems reported in the 23 other counties that are using DRE machines, he said. But in each case, the errors were caught and corrected by the voter, he added.

"Improperly calibrated machines do not default in a manner that causes Republican votes to be recorded as votes for other candidates, Democratic or Libertarian," he wrote.

The software is programmed to highlight only those candidates whose names the voter actually touched. The machine may not accurately reflect the voter's intent if it has lost its calibration, Bartlett said. But as a safeguard every DRE voting system used in the state prompts the voter to verify their vote, he said.

Election watchdogs have for some time expressed concerns about DRE systems. Many academics, researches and election watchdog groups such as Verified Voting and Common Cause have said that such systems are prone to errors of the sort claimed by the RNC.

They have claimed that such machines are susceptible to tampering and accidental failure.

Many of the concerns are directed at DRE systems that lack so-called voter verifiable paper audit trails (VVPAT).

Election watchers have said that paperless DRE system pose a special threat to the integrity of the elections because they offer no easy way for a post election audit of the results. More than half of all states are scheduled to use DRE's to varying extents next Tuesday. Seventeen of them use paperless DREs in at least some areas.

Concerns about DRE systems aren't restricted to one party. During the 2008 presidential election, at least 16 voters in six counties in West Virginia reported having their votes for Obama being switched to votes for Sen. John McCain, according to a report by Verified Voting earlier this year. In June 2011, during the Democratic primaries in New Jerseys Cumberland County, a paperless DRE system attributed votes to the wrong candidates and ended up declaring the actual losers as winners of the election, according to Verified Voting.

Although Republicans are raising questions now, both sides have weighed in on the issue of e-voting this year. Democrats recently questioned the propriety of investment ties between a company run by one of Romneys sons and Hart Intercivic.

Hart Intercivic is a voting machine manufacturer whose systems are set to be used widely in several states next week.

Jaikumar Vijayan covers data security and privacy issues, financial services security and e-voting for Computerworld. Follow Jaikumar on Twitter at @jaivijayan, or subscribe to Jaikumar's RSS feed . His e-mail address is jvijayan@computerworld.com.