The Web site was created and operated by Pennsylvania's Department of State and was taken down on Tuesday after officials became aware of the problem, department spokeswoman Rebecca Halton said.

Halton said the department had not yet determined how many applications were viewed - or how many people viewed them - but stressed that state officials were working to determine that and would contact any voter whose information may have been accessed.

The department, Halton added, is "taking steps to ensure this doesn't happen again."

The security problem, she said, will not affect the validity of applications that were printed from the site and mailed in. Nonetheless, it did give anyone with computer savvy - whether a next-door neighbor or a political operative - the ability to see applications that contained the personal information.

The glitch was brought to the attention of state officials by Robert McMillan, a reporter for IDG News Service, a technology news wire.

In an interview yesterday, McMillan said he discovered the flaw after reading a posting on the Internet rating site Digg.com that suggested there was a security problem with the state's Web site.

Intrigued, McMillan hopped onto the site and was able to view almost a dozen applications - and likely could have seen thousands if he had had the time or the will.

To understand how McMillan, and possibly other members of the public, were able to view the applications, it is necessary to understand how the Web site worked. Residents were asked to type in their information, including name, home address, driver's license number and party affiliation. The site then created PDF computer files that they could print out, sign and mail in. The application could not be submitted electronically.

The site has been heavily used, particularly in the last few months leading up to the state's April 22 primary contest between Sens. Hillary Rodham Clinton and Barack Obama. Since the beginning of the year, more than 90,000 residents have completed the form online, half of them this month alone.

McMillan said that once the system created the PDF file, it assigned it a Web address that included a personal reference number. The voter could then manipulate that number to view previous applications.

McMillan said he changed the number to view applications that, sequentially, were numbered tens of thousands earlier than his.

Halton, of the Department of State, could not definitively say what the glitch was, only that the state responded swiftly once it became aware of it.

"It's a very exciting year to participate in the political process," she said, "and we will do everything we can to make sure that it's an enjoyable and secure process for voters."