U.S. banks have been buffeted by more than a week of powerful cyberattacks. The mystery surrounding their perpetrators lingers. One expert said that he was suspicious of claims of responsibility purportedly made by Islamists angry at an anti-Muslim movie made in the United States. The widely-circulated Internet postings might have been an attempt to deflect attention from the true culprit. "In the intelligence world, we call that a `false flag,'" said Mike Smith, whose Web security company Akamai has helped analyze some of the attacks.