USA Today via Voter Action:

With the primary elections approaching, six states have lawsuits pendng to end the purchase and use of computerized electronic voting machines. Voter Action filed Thursday against Colorado (and nine counties).  There were similar lawsuits in California and Arizona this spring and New Mexico last year. Others targeted computerized electronic voting in Florida, Ohio and Pennsylvania. Six of these states will be using some touch screen voting machines.

Claims being made are the machines are vulnerable to software tampering, don’t keep a recountable printed record, may miscount, switch/not record votes, and add phantom votes.

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In California, where a primary is Tuesday, after a March lawsuit, several counties switched to printed ballots that will be counted with optical scanners. Six of the eight states will have some electronic balloting, which records votes by touch screens.  In addition, Texas and Illinois had problems with electronic voting machines during their primary elections.  

According to Electronic Data Services (EDS),one-third of the USA’s 3,114 counties use some type of electronic systems.  Half the counties use optical scanners which read dots or mark that voters pencil in on ballots.  Parts of New York and Connecticutt use lever type voting machines and some smaller communities use hand-counted paper ballots.

There has been no litigation specifically claiming the intentional manipulation of electronic voting, however, according to Black Box Voting, a Finnish expert found security flaws for a Diebold Election Systems model.

Although electronic voting was used for over five years, it was not widespread until after 2002, when Congress passed the Help America Vote Act (HAVA). HAVA required states to replace old voting methods such as punch cards as the results of the 2000 election in Florida are questionable. Congress gave states over than $300 million to replace older voting systems.  
Although the funding was allocated, it was not used in Ohio.  

As written by Robert F. Kennedy Jr.,

Under the Help America Vote Act, Ohio received more than $30 million in federal funds to replace its faulty punch-card machines with more reliable systems.(137) But on Election Day, that money was sitting in the bank. Why? Because Ken Blackwell had applied for an extension until 2006, insisting that there was no point in buying electronic machines that would later have to be retrofitted under Ohio law to generate paper ballots.(138)

As more questions re:  the 2004 elections have been raised,

we simply cannot be certain that the right man now occupies the Oval Office — which means, in effect, that we have been deprived our faith in democracy itself.

Despite this, Paul DiGregorio of the federal Election Assistance Commission admits there are glitches but claims the system “can be trusted” if safeguards are in place. Although, nothing is stated to what those safeguards are.

Diebold, says the vulnerability is theoretical and will be fixed this year.

Oher defenders of electonic voting claim that problems occur because of hasty set-up before elections or poor training of poll workers. R. Doug Lewis of the Election Center, a group of state and local election officials,

“Certainly none of the allegations of security breaches on the equipment have ever been demonstrated to be true.”

If Lewis is referring to a court of law in his statement he is technically correct.

For now.