The Department of Defense announced that Specialist [Bradley] Manning, of Potomac, Md., had been arrested and was under investigation [for leaking a video of a US helicopter attack on civilians in Baghdad to a whistleblower website, Wikileaks]. The leak of the helicopter video, which Wikileaks titled "Collateral Murder," caused serious consternation at the Pentagon, where senior officials are increasingly concerned about technology that makes it easier to anonymously post documents, photographs and videos online. But opponents of the Iraq war have said that the video provided irrefutable evidence of a military blunder, and that it should not have been classified. The episode also drew wide attention to Wikileaks, a once-fringe Web site that aims to bring to light secret information about governments and corporations. It was founded three years ago by Julian Assange, an Australian activist and journalist, and has published documents about toxic dumping in Africa, protocols from Guantánamo Bay and e-mail messages from Sarah Palin's personal account.