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Google is the target of a trojan that could be more damaging than the worm that has affected literally dozens of Orkut users. This new trojan, however, hits Google where it hurts — its ever-swelling advertising revenues. It redirects Web ads from the AdSense program to a rival ad provider. Bitdefender, the Romanian security-software maker which identified the trojan, does not specify who is serving these third-party ads or how the trojan is propagating. Researchers do say that Google may be powerless to stop the attack, because the malware affects personal computers, not the company's ad servers. Google is unlikely to lose substantial sums, but the search giant cannot enjoy being this helpless. No wonder it's pushing antivirus software.