The feature allowed users to find people's names and addresses, depending on whether they were listed, by punching in their telephone numbers. While the information is available from other sources--such as CD ROMs and special phone books--many relied on Yahoo's easily accessible service to do things such as looking up otherwise unidentifiable numbers that appeared on their phone bills.
Others used it for more serious purposes: At least one agency used it to help identify suicide and other victims.
Yahoo pulled the site in response to email sent recently by a few dozen people complaining that the site invaded their privacy, Henry Sohn said. Sohn is the Yahoo senior producer who launched the feature.
For instance, a person running a classified ad might have her phone number printed and leave out her name and address. But if she were listed, anyone could use Yahoo's service to find out who she was. The ability to identify someone's phone number through caller ID also has made people more sensitive to the issue, Sohn said.
Yahoo decided to "err on the side of privacy," Sohn said, at least for now. Yahoo now is taking a "wait and see" attitude about the service, and there are no plans to reinstate it. "At least until there's more comfort level we should hold off on it for a while."
But if the amount of email has any bearing on the service's fate, the balance is tipped in favor of bringing it back.
Since Yahoo pulled the site about a week ago, it has received hundreds of emails from people who miss it, Sohn said.
Some, such as Robert Mang, a manager at Nynex phone company in New York, said they depended on it.
Mang said he used the service to help suicide hotlines, police and other agencies track down calls. Nynex traces the calls but then has to find the point of origin--based on the phone number. It isn't always an easy task.
"We have our own systems to look that up," Mang said. "Sometimes it's slow because of the login practice." Also, he said, sometimes calls come from small telephone companies that close in the middle of the night, when Mang is on duty.
Up until a week ago, Mang's practice had been to go into Yahoo's service first. If he couldn't find the information, he'd then log into his own system, a fairly cumbersome if more secure process.
There have been times when Yahoo's service has saved an estimated 20 minutes. Mang can't say for sure, but he's convinced that the service has made a difference.
"If somebody's cut their wrists and said, 'I'm committing suicide,' that 20 minutes could make the difference between life and death," Mang said. "Twenty minutes is a long time when you're bleeding."
Mang also has told police departments about Yahoo's service. Although they have CD ROMs with reverse directories, the discs aren't always up to date--and aren't always easy to find, Mang said.
But other users of the service might not always have such lofty goals, Sohn said, citing the emails.
Privacy experts worry about services that give people virtually unlimited access to data bases that once had limited access.
"Sort of the idea that every teenage kid on the net can plug in a number and find out it's yours is different," said Karen Coyle, Western regional director of Computer Professionals for Social Responsibility.
"If your phone number has become known in some way that's outside of your control, then it allows people to identify you," Coyle said. "It gets harder and harder to communicate without losing your privacy. That is the thing that is scary."
Coyle added that public agencies should be given the capacity to properly do their jobs and shouldn't have to rely on the Internet for crucial information.
Meanwhile, anyone who logs onto Yahoo looking for the service will be greeted with a People Search page containing only the usual form to look up people by name and address. A link at the bottom leads to a brief online explanation.
"We have elected to discontinue the reverse lookup feature because of privacy concerns that have been raised by users," it states.