It's not what other people think of you that matters. It's what they can find out about you on the Web that will affect your ability to get a job or promotion, rent an apartment, buy a house, be accepted into the school of your choice, or find the love of your life.

Increasingly, your personal reputation is at the mercy of search engines, blogs, and social networks, none of which themselves have a sterling reputation for accuracy.

Identity theft, libel, defamation, mistaken identity, and youthful indiscretions captured forever—these are just a few of the things that can come back to bite you.

Fortunately there are ways to fight back—five ways, in fact. And it all starts with discovering the depth and breadth of your personal Net footprint.

1. Google Yourself

It's not enough to have the respect and admiration of your family and your peers; you need Google juice as well. Because if someone Googles your name and finds nasty things written about you, your credibility could be destroyed in an instant. The postings could be the rantings of a disgruntled former employee or an angry ex-spouse, or of someone posing as you, or even someone with the same name—in any case, you're toast.

"Google is no longer just a search engine; it's a reputation engine," says Chris Dellarocas, a professor at the University of Maryland who studies online reputations. The first step in taming this beast is to find out what's out there by Googling all variants of your name, your phone number, and your address.

If you've put stuff on your own sites that you don't want Google to find, you can ask the search engine to delete it from its results. If someone else posted this material, though, Google won't remove it. You'll have to ask the site owner to take it down—or hire someone to do it for you (see item #5).

2. Comb the Web

Even the mighty Google can't catch everything. For example, many of Facebook's 60 million profiles are inaccessible to search engines. So even if you haven't created a page on Facebook, MySpace, or one of the gazillion other social networks, someone else might have set up a spoof page to make you look bad.

Start by looking at so-called "people search" engines. Sites like Pipl, Spock, Wink, and ZoomInfo scrape information from other Web sites (like social networks) and slap it together into personal profiles. It's not uncommon for such sites to mix information about different people with the same name and present them as a single person. That's not so good if you've got the same name as, say, a porn star or a disgraced former Congressman.