Companies have long used criminal background checks, credit reports and even searches on Google and LinkedIn to probe the previous lives of prospective employees. Now, some companies are requiring job candidates to also pass a social media background check. A year-old start-up, Social Intelligence, scrapes the Internet for everything prospective employees may have said or done online in the past seven years. Then it assembles a dossier with examples of professional honors and charitable work, along with negative information that meets specific criteria: online evidence of racist remarks; references to drugs; sexually explicit photos, text messages or videos; flagrant displays of weapons or bombs and clearly identifiable violent activity. The service ... alarms privacy advocates who say that it invites employers to look at information that may not be relevant to job performance. And what relevant unflattering information has led to job offers being withdrawn or not made? Marc S. Rotenberg, president of the Electronic Privacy Information Center, ... said that employers were entitled to gather information to make a determination about job-related expertise, but he expressed concern that "employers should not be judging what people in their private lives do away from the workplace."