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The South Carolina inmates filled their time posing as women and scrolling social media and dating sites until a few key details caught their eyes.

Cropped hair. Proximity to military bases. Maybe a photo or two in uniform.

Then, the messages to entrap and blackmail service members began from within the walls of South Carolina correctional facilities, crafted with a simple and terrifying scheme, authorities said.

After romantic messages and racy photos were exchanged, prisoners would pose as the fictitious girl’s father, telling victims that she was underage and the images constituted child pornography.

Pay money to make it go away, the inmates demanded, or police would be notified.

In all, 442 troops from across the country fell prey, paying out more than $560,000 in the “sextortion” scheme, authorities said Wednesday, after five arrests and 15 indictments in the wake of a crackdown on an elaborate network.

“With nothing more than smartphones and a few keystrokes, South Carolina inmates along with outside accomplices victimized hundreds of people,” Daniel Andrews, an Army investigator focused on computer crimes, said in a news release.

Operation Surprise Party was launched in January 2017 by the Naval Criminal Investigative Service, officials said, and later joined by Army, Air Force, state and federal agents. The announcement marked the first phase of the operation, though it is unclear when the investigation began or what alerted authorities to the practice.

More than 250 other people are under investigation and could face charges, said Jeff Houston, an NCIS spokesman.

Victimized troops paid out of fear that their careers would be jeopardized by the fake claims, officials said. Sometimes blackmailers would also pose as police. It is not clear how the extortion ring grew so elaborate or how inmates were marshaled into the operation.

NCIS could not say why troops were specifically targeted. It is possible schemers leveraged feelings of integrity and professionalism to shame military personnel. And troops are subject to both civilian and military laws — which could raise the perception that a crime would be even more personally and professionally catastrophic.

Online romance scams have frustrated military officials for years, as they disrupt military duties and erode resources.

In one common scheme, scammers steal online photos of fit men in sharp uniforms and post them on dating sites. Women looking for romance are taken in by invented stories of widowers or single parents on combat deployments and in need of money, said Christopher Grey, a spokesman for the Army’s Criminal Investigation Command.

Stories of wartime danger with a tinge of romance helped sell the scam. And the unpredictability and long duration of deployments provided a baked-in excuse for scammers to never quite meet or speak on the phone, Grey told The Washington Post on Wednesday.

In past years, angry calls flooded military investigator offices and other commands. Women wanted information on troops who took money and disappeared. But the troops were unwittingly used, Grey said.

The calls still come, Grey said. But increasingly, suspicious targets now call to check whether a wartime love story is just too good to be true.

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