Ms. Alexander and many Internet activists have good reason to be queasy. California’s Political Reform Act of 1974, and laws like it across the country, sought to cast disinfecting sunlight on the political process by requiring contributions of more than $100 to be made public.

Image A Web site takes names and ZIP codes of donors supporting the measure and overlays data on a map.

Eightmaps takes that data, formerly of interest mainly to social scientists, pollsters and journalists, and publishes it in a way not foreseen when the open-government laws were passed. As a result, donors are exposed to a wide audience and, in some cases, to harassment or worse.

A college professor from the University of California, San Francisco, wrote a $100 check in support of Proposition 8 in August, because he said he supported civil unions for gay couples but did not want to change the traditional definition of marriage. He has received many confrontational e-mail messages, some anonymous, since eightmaps listed his donation and employer. One signed message blasted him for supporting the measure and was copied to a dozen of his colleagues and supervisors at the university, he said.

“I thought what the eightmaps creators did with the information was actually sort of neat,” the professor said, who asked that his name not be used to avoid becoming more of a target. “But people who use that site to send out intimidating or harassing messages cross the line.”

Joseph Clare, a San Francisco accountant who donated $500 to supporters of Proposition 8, said he had received several e-mail messages accusing him of “donating to hate.” Mr. Clare said the site perverts the meaning of disclosure laws that were originally intended to expose large corporate donors who might be seeking to influence big state projects.

“I don’t think the law was designed to identify people for direct feedback to them from others on the other side,” Mr. Clare said. “I think it’s been misused.”

Many civil liberties advocates, including those who disagree with his views on marriage, say he has a point. They wonder if open-government rules intended to protect political influence of the individual voter, combined with the power of the Internet, might be having the opposite effect on citizens.