It can take a long time — if ever — to undo damage caused by comments on the Internet. Scathing posts can tarnish reputations for people and businesses, and the snarkiest stuff can go viral before you know about it. That's why it's good for job applicants, professionals, business owners and public relations professionals to do frequent search engine sweeps to see what's out there about you (or could be confused with you).
You may need a lawyer to help remove libelous stuff. But you also might be able to counter unfavorable postings without lawsuits or threats.
If a posting is provably false, you may have luck asking the site's webmaster to remove it. Many webmasters, though, will say they're not in the business of dispute resolution and won't delete a comment simply because you want it gone.
Some comment victims have used Google's tool that flags offending URLs, paving the way for Google crawlers to eventually drop an offending URL from search results. But that won't work for, say, bad reviews that are posted on legitimate comment sites such as Yelp.com.
Some companies and people hire reputation- or brand-management companies. These firms do online searches and help respond to unfavorable posts. That includes generating positive posts to counter negative ones. Just don't get caught writing your own glowing reviews; that's an ethical minefield.
Your posted responses should be factual. Businesses countering a bad review should apologize if warranted and offer a resolution if possible. It's also fine to ask satisfied customers to write reviews, perhaps crowding out the bad ones.
People who are damaged online might do better responding offline. If you think a prospective or current employer is seeing bad things about you, use the phone, email or regular mail to rectify rather than staging a war of words online.