Twitter users have caused an uproar by impersonating celebrities on the popular micro-blogging service. Businesses, too, are targets of fake Twitter profiles -- sometimes from competitors.

Exxon Mobil Corp. has found at least two unauthorized Twitter accounts under variations of its name. Twitter -- a networking service where users create profiles and send out short messages, or "tweets" to their followers -- terminated one of the profiles last summer. An Exxon spokesman says the oil company is considering what to do about the second profile, which it discovered several weeks ago. The profiles didn't appear to contain malicious content...