(Screenshot/Familytreenow.com)

Early Tuesday morning, Anna Brittain got a text from her sister: Did she know about Familytreenow.com? The relatively unknown site, which presents itself as a free genealogy resource, seemed to know an awful lot about her.

“The site listed my 3- and 5-year-olds as ‘possible associates,’ ” Brittain, a 30-year-old young-adult fiction writer in Birmingham, Ala., told The Washington Post on Tuesday. Her sister, a social worker who works at a child advocacy center, found the site while doing a regular Internet footprint checkup on herself. “Given the danger level of my sister’s occupation,” Brittain added, the depth of information available on the genealogy site “scared me to death.”

There are many “people search” sites and data brokers out there, like Spokeo, or Intelius, that also know a lot about you. This is not news, at least for the Internet-literate. And the information on FamilyTreeNow comes largely from the public records and other legally accessible sources that those other data brokers use. What makes FamilyTreeNow stand out on the creepy scale, though, is how easy the site makes it for anyone to access that information all at once, and free.

Profiles on FamilyTreeNow include the age, birth month, family members, addresses and phone numbers for individuals in their system, if they have them. It also guesses at their “possible associates,” all on a publicly accessible, permalink-able page. It’s possible to opt out, but it’s not clear whether doing so actually removes you from their records or (more likely) simply hides your record so it’s no longer accessible to the public.

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Unusually for a site like this, FamilyTreeNow doesn’t require a fee, or even the creation of an account, to access those detailed profiles (assuming, of course, that person hasn’t already opted out). Lexis Nexis, for instance, can also aggregate tons of public records to create an in-depth profile of a person. But that service is cost-prohibitive to most people who don’t have access to the site through an institutional subscription.

Sure, a free database aggregating thousands of U.S. public records could be beloved by genealogy hobbyists across the country. But the site is also extremely useful to those who might want to harass or physically harm someone else — and that, it seems, is what is freaking a lot of people out about it.

After reading the text from her sister, Brittain pulled up her own profile and immediately opted out of having her information included on the site. Then she composed tweets, warning others and providing detailed instructions on how to do the same. The top of her thread on FamilyTreeNow had thousands of retweets by the end of the day.

A similar warning about FamilyTreeNow also popped up on “Enough is Enough” and “Survive the Streets” this week,