From the beginning, the Internet has attracted people seeking to research their family trees — and sites wanting to make money off their pursuits. The Web's search capabilities seemed custom-tailored to sorting through long-forgotten records that are now being dusted off and digitized. Hundreds of sites sprang up.

In practice, though, Web genealogy has led to a lot of frustrated consumers — the process has been expensive (most sites charge fairly steep subscription fees) and time-consuming.

Now, sites are aiming to eliminate some of those drawbacks. One new entrant, Geni.com, which was launched last month by a former PayPal executive, offers a new model, based on connecting living relatives free of charge. The site is part genealogy, part six degrees of separation: Instead of paying a fee to research family records buried in archives, it asks users to build their own family trees — using the knowledge of living relatives — that eventually will merge into one giant family tree for the world. That is the hope anyway.

Geni.com is taking some of the elements of popular so-called social-networking and user-generated content sites such as Wikipedia and MySpace. It went live in mid-January and has registered more than 100,000 users since then. It has done no traditional marketing yet, but blogs such as Digg (where users submit news stories) and Tech Crunch (which focuses on technology) passed the word. The site is free. Rather than charging fees, Geni plans on selling advertising and also plans to generate revenue by creating "premium" accounts and selling products, such as posters or coffee-table books of the family trees.

But Geni has already courted controversy — and raised privacy concerns. Several blog posts have expressed frustration with the level of personal information that can be published about a person, even without their permission. For example, a Geni member can create entire profiles for relatives who don't visit the site, including their birth dates, education, phone number and photos. Some of the identifying pieces of information used by many financial institutions — such as mother's maiden name and birth date — are often listed on the site.

To address those concerns, Geni is only allowing visitors to the site to see their own family trees. Geni says that family members are responsible for ensuring that the profile information is correct. (Popular sites such as MySpace rely primarily on similar modes of self-policing.) The company says it doesn't plan to sell the data to marketers. It also says it will introduce more privacy features as the site grows.

Ben Guthro, a 27-year-old software engineer from Boston, started building a family tree on Geni.com after he saw a post on Digg. His tree now has 250 members, some of whom he has never met before, such as his mother's cousin who lives in California. "It spreads fast," he says.