BOSTON ( TheStreet) -- In his 1980s-era cartoon series, G.I. Joe would end each show with these wise words: "Knowing is half the battle." This is especially true for those trying to protect their personal or professional reputations online.

"Before you can begin to manage a reputation, you have to figure out what's being said," says B.L. Ochman, director at Proof Digital Media, the online media arm of the public relations agency Burson-Marsteller.

With the abundance of social media sites out there, it takes more than a simple Google ( GOOG) search to keep abreast of who's trashing or praising you on the Web. Several startups are making a living in the reputation management field, but for those who don't want to pay for the service, here are five free reputation monitoring tools.

ReputationAlerts: Still in the beta-testing stage, this service from Reputation Defender is similar to Google Alerts; it trolls the Web for new mentions of you and sends out periodic e-mail alerts. But it goes a step further by separately searching for personal information about you that could lead to identity fraud, such as mentions of your age and address. Future iterations of the product will include ratings of your social influence and the public's general perception of you, based on how others portray you on the Web.

TweetBeep: Basically Google Alerts for Twitter, it keeps track of Tweeted mentions of you or your company or any other word or phrase you want to monitor. A free version of the service will keep track of five keywords and send you daily alerts with a maximum of 50 results. The Premium service, which costs $20 per month, keeps track of up to 50 keywords and includes hourly and daily alerts that include up to 1,000 results.

OneRiot: OneRiot is kind of a one-stop zeitgeist tracker, helping companies and potential advertisers keep track of topics being discussed on social networking sites such as Twitter, Digg, MySpace and Facebook.

BlogPulse: While this tool primarily is used for trend discovery -- for instance, what's hot today -- it also can be used to discover mentions of you or your company in the blogosphere, giving you have a chance to respond and defend yourself in blog comment sections.

FollowerWonk: This tool lets you search for Twitter users according to keywords in their Twitter bios. This is a good way to sniff out imposters: Twitter users pretending to represent your company online, such as BP ( BP) parody " BP Global PR" and " ATT Parody Relations."

-- Written by Carmen Nobel in Boston.

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