systems, can be difficult to implement, often require specialized external hardware, and can be difficult to use. In the United States twenty-seven states require a paper audit trail by statute or regulation for all direct recording electronic voting machines used in public elections. Another eighteen States don't require them, but use them either statewide or in local jurisdictions. Security concerns The introduction of malicious software into a VVPAT system can cause it to intentionally misrecord the voter's selections. This attack could minimize detection by manipulating only a small percentage of the votes or for only lesser known races. Another security concern is that a VVPAT could print while no voter is observing the paper trail, a form of ballot stuffing. Even if additional votes were discovered through matching to the voters list, it would be impossible to identify legitimate ballots from fraudulent ballots. Alternatively the printer could invalidate the printed record after the voter leaves and print a new fraudulent ballot. These ballots would be undetectable as invalidated ballots are quite common during elections. Also, VVPAT systems that are technically able to reverse the paper feed could be open to manipulated software overwriting or altering the VVPAT after the voter checks it. Usability and ergonomic concerns For the voter, the printed record is "in a different format than the ballot, in a different place, is verified at a different time, and has a different graphical layout with different contrast and lighting parameters." In November 2003 in Wilton, CT, virtually all voters had to be prompted to find and verify their receipt, increasing the time required to vote and the work for the pollworkers. The VVPAT adds to the complexity of voting, already a deterrent to voting. In addition, a VVPAT component may not be easily usable by poll-workers, many of whom are already struggling with DRE maintenance and use and new elections law requirements. In the 2006 primary election in Cuyahoga County, Ohio, a study found that 9.6 percent of the VVPAT tapes were either destroyed, blank, illegible, missing, taped together or otherwise compromised. In one case the thermal paper was loaded into the printer backwards leaving a blank tape, which was not realized by voters who couldn't verify the paper trail. The Cuyahoga Election Review Panel proposed in its final report to remove the opaque doors covering the VVPAT except the ones equipped with equipment for blind voters. In