Wired posted quite a scoop last night: Specialist Bradley Manning, a 22-year-old Army soldier deployed to Iraq, has been arrested in a probe of the leaking of a video that showed the graphic deaths of journalists and civilians at the hands of a U.S. helicopter in 2007. The video was packaged and published by WikiLeaks, a collectively managed website that provides safe harbor to undisclosed information and those who seek to expose it.

According to Wired reporters Kevin Poulsen and Kim Zetter, Manning asked a relative to post the following message on his Facebook page:

“Some of you may have heard that I have been arrested for disclosure of classified information to unauthorized persons. See CollateralMurder.com.”

How did the arrest happen? Adrian Lamo, a high profile ex-hacker, told Wired that Manning contacted him via instant message in the last couple of weeks, and claimed responsibility for providing the site with a variety of goods: the Iraq video, another yet unreleased video of an Afghan airstrike that may have killed around 100 civilians, an army intelligence report that assessed WikiLeaks’s impact on information security, and a previously undisclosed trove of hundreds of thousands of State Department diplomatic documents.

Lamo, who says he was especially concerned with security implications of releasing the diplomatic cables, says he contacted the FBI and shared their chat logs.

Julian Assange, the public face of the increasingly high-profile site, has bragged about his organization’s record of protecting its sources from legal trouble as a result of their decisions to provide documents.

“All our sources have not been exposed, as far as we know. Certainly none have been publicly exposed,” he said just last Thursday in a conference appearance, adding that “Almost no one gets caught. Almost everyone is successful in leaking the material.”

Barring unforeseen developments, it would appear that this arrest blemishes that claim.

Though that blemish could come with a caveat. Lamo says the FBI told him the arrest of Manning came only after he first contacted the bureau, meaning that it’s entirely possible this arrest would not have happened if Manning had not been careless by sharing his story with Lamo. That would be a security breach on Manning’s part, not on WikiLeaks’s.

Clint Hendler is the managing editor of Mother Jones, and a former deputy editor of CJR.