"The biggest problem we had to solve was the privacy problem," Mr. Gilmour said.

Because the information used to determine if someone is an expert on a particular question stays on local computers, Tacit's executives said Illumio would avoid potentially troubling privacy questions. The Illumio software is installed on users' PC's, where it is connected through a software interface to either Microsoft or Google's desktop search programs that index local user content, including documents and electronic mail.

The anonymity offered by Illumio is a significant advantage over other social networking software services that place pressure on users to offer assistance.

The Illumio software uses a reverse auction model to restrict the answer to the best expert. In a reverse auction, sellers compete for the right to provide goods or services. For example, in response to the question, "Who knows John Smith?" each Illumio local system would independently determine who had the best relationship in the network based on parameters such as who had recently exchanged the most e-mail with John Smith.

If the local system found a strong relationship, the local Illumio client software would pop up a request on that user's screen asking whether the user wished to respond to the person asking the question. Initially only the strongest candidates would be notified locally of the query. If that user ignored the request, the reverse auction system would, in effect, lower the bar to ask the person with the next strongest relationship. Then, if there were no responses, the bar would be again lowered until an expert responded. It is possible that difficult questions would find no experts.

The system insures that experts remain anonymous until they agree to answer the query. When a user answers, the connection is made either through the Illumio system, by e-mail or by other channels such as instant messaging or telephone.

In addition to the keywords that make up the question, a user is permitted to send an accompanying message that will help people determine whether they have relevant information to a particular question.

Tacit hopes to market the service by providing Web masters with icons it calls "hot spots." For example, a person running a digital photography or similar Web site could place a hot spot on its home page and then anybody who wanted to join an Illumio network on digital photography could do so by simply clicking on the link.