Security threats may lurk in seemingly innocuous Web pages. Legitimate sites may get hacked, cybercriminals game search engines to make sure that their infected pages come up in searches for hot topics (a technique known as "search engine poisoning"), and seemingly safe sites may harbor malware. Although you have no way to guard against these attacks completely, using a link checker can help protect you from many of them.
Link-checker tools typically show small badges next to links in search results and elsewhere to indicate whether a site is trustworthy, dangerous, or questionable. Many such tools also add a status indicator to your browser's toolbar to signal the presence of any problems with the site that you're currently visiting.