If Sherlock Holmes were a genealogist, Internet sleuthing could keep him really busy. Although ancestral clues abound on millions of family history Web sites, online roots research isn't exactly elementary: Finding the missing links to your past involves more than simply clicking to those clues. You still need to verify what you find online—even if Aunt Sophia's purported birth date sounds right or you're pretty sure Great-uncle Frank grew up in Detroit. Researchers of all experience levels publish on the Net, and errors do crop up. No genealogy gumshoe wants to trace the wrong ancestor because someone didn't get his facts straight. So how do you separate the good online data from the bad and the ugly? Follow these six steps to track down reliable information about your ancestors.

Step 1: Assess the data.
Identifying the type of information you find on the Net will help you determine how to verify it. Professional genealogists typically label sources primary or secondary, or original or compiled. Original, or primary, sources are those created at or close to the time of an event, by someone who had personal knowledge of it. Birth records, wills, deeds, passenger lists and census records qualify as original records. That's not to say that they're always 100 percent accurate, though—any record can contain errors. Compiled, or secondary, sources include online databases, published family histories and county histories.

When we say "original," that doesn't mean you have to look at the actual document that was created 50 or 100 years ago. A photocopy, microfilm or digital image of that document works just as well. In fact, digitized versions are sometimes better than the originals because they've been enhanced for readability.

Although more and more digitized records are appearing online, they represent just a fraction of all the family history sources available. Most Web data has been pulled from other sources to create an abstract or searchable index or database. Online indexes can make your research much easier, just as book indexes do. But you wouldn't look up something in a book index, copy down the information, then close the book without checking the cited page—and you should apply the same principle to checking Web data. When you find your ancestor in an index, jot down all the data, and then look for the original source of that information.

Finding your ancestor in a database may be your first hurdle, though. Spelling variations and other mistakes abound on the Net because transcribers generally create databases from original, handwritten records, which aren't always easy to read. When I searched Ellis Island's passenger-lists database for Michael Concannon, who had emigrated from Ireland in 1905 at the age of 25, the closest match was a Michael Concanmon, age 75. I took a chance and looked at the original passenger list—and I'm glad I did. The manifest listed his age as 25; the transcriber must have misread it. (Of course, the lesson here is always look at the original record yourself.)

It's no surprise that online databases and indexes generate problems with name spellings. Your ancestor's name—even if it's a common one—could have been entered incorrectly into the database, in which case you might never find that person. Even just a simple transcription mistake, such as transposing two letters or adding a letter—Havrey Miller or Harvey Imller or Harvey Milller—can send your ancestor into the black hole of cyberspace, never to be seen or heard from again. But assuming you're lucky enough to find your ancestor's name, it's important to verify the data, so you know you have the right person and the right information.