A tip-off from Microsoft has led to the arrest of a man in Pennsylvania who has been charged with receiving and sharing child abuse images.
It flagged the matter after discovering that an image involving a young girl had been allegedly saved to the man's OneDrive cloud storage account.
According to court documents, the man was subsequently detected trying to send two illegal pictures via one of Microsoft's live.com email accounts.
Police arrested him on 31 July.
The man, in his twenties, has since been placed in a county correctional facility and has yet to enter a plea. A preliminary court appearance is scheduled for next week.
A copy of the affidavit detailing the case against the defendant has been published online by a news site specialising in leaked law enforcement documents.
It claims that the man acknowledged acquiring the pictures through Kik Messenger, a chat app, as well as "trading and receiving images of child pornography on his mobile cellular device".
The BBC spoke to one of the officers involved, Trooper Christopher Hill from the Pennsylvania State Police, who confirmed the affidavit was genuine and that Microsoft had instigated the investigation.
Illegal images were allegedly found on the man's OneDrive cloud storage account
But he said he could not discuss any of the case's specifics because it was still an "open investigation".
He did, however, add that he was aware of other instances of "internet carriers" passing on similar details in other inquiries.
Automated image scans
The details have emerged a week after it was first reported that Google had handed over the identity of a Texas-based user after detecting suspected child abuse imagery in his Gmail account. The 41-year-old was arrested as a consequence of Google's action.
The cases highlight the fact that commonly-used internet services are not private.
One campaign group said tech firms must be explicit about how they monitor users' accounts.
"Microsoft must do all that it can to inform users about what proactive action it takes to monitor and analyse messages for illegal content, including details of what sorts of illegal activity may be targeted," commented Emma Carr, acting director of the campaign group Big Brother Watch.
"It is also important that all companies who monitor messages in this way are very clear about what procedures and safeguards are in place to ensure that people are not wrongly criminalised, for instance, when potentially illegal content is shared but has been done so legitimately in the context of reporting or research."
Microsoft's terms and conditions for its US users explicitly state that it has the right to deploy "automated technologies to detect child pornography or abusive behaviour that might harm the system, our customers, or others".
Disrupting photo trades
Neither Google nor Microsoft handed over the material directly to the police.
Instead both companies contacted the National Center for Missing and Exploited Children's CyberTipline, which serves as the US's centralised reporting system for suspected child sexual exploitation. ..Continued.. by Leo Kelion
