President Barack Obama and his Republican challenger, Mitt Romney, have adopted an online advertising tactic referred to as brand hijacking that companies have used for years to market wares to Web users searching for information on competitors, Bloomberg reported.

People who typed one candidate’s name into Google Inc.’s search box in some markets have seen ads for his opponent. A search for “Barack Obama,” for instance, has yielded ads for Romney, while entering “Mitt Romney” has resulted in ads for Obama. Romney has used a similar tactic on Facebook Inc.’s site.

The approach is designed to help the candidates raise awareness among users of the Web or social networks. Used by companies, the practice has also stirred controversy, resulting in lawsuits that alleged it enables trademark violation. Though court rulings have been mixed over whether this form of advertising technique is legal, it can breed confusion for voters seeking information about one candidate to be shown ads for another, said Peter Harvey, an attorney at Harvey Siskind LLP.

“There are some real negatives in terms of causing consumer confusion and misdirecting people,” said Harvey, who practices intellectual property law. “And it’s quite intentional. So, it’s a problem.” Read more.