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Bitcoin blackmail: Letter threatens to tell the world your secret

OKLAHOMA CITY - The note is addressed to Cassie Bowen and reads like someone is trying to blackmail someone.

"I have evidence of what you have been hiding," it reads.

The letter was sent to Cassie’s home.

"It is just your bad luck that I stumbled across your misadventures," it continues.

Cassie is happily married and faithful, to a man.

She said, “So they obviously didn't know Cassie was female.”

They're going after cheating spouses and their objective is to get them to give up some major coin in the form of cryptocurrency.

"If you want me to keep your secret, then send 3,500 in bitcoin," the letter continued.

Luckily for Cassie, the scammer includes front and back instructions for her on how to buy bitcoin.

"The amount of money is such, that it's not so much that someone might be willing to just pay that to make it go away," said Patrick Wyman, a supervisory special agent with the FBI's money laundering unit. "They're hoping that they might get lucky with someone who actually … [has] some infidelity there. And if they hit that target, that's a person who's probably willing to pay."

In an interview with CNBC, Wyman said the idea behind virtual currency is that it hides behind the veil of secrecy.  

"Just because it's letters and numbers in terms of an account number, and there's no personal information associated with it, that law enforcement won't be able to track it," said Wyman.

The note targeting Cassie showing up in an envelope with a stamp, but no postmark.

She and her husband went back to review their security camera footage.

“We didn't see anyone other than the postman coming to our mailbox for a few days before and the day of,” she said.

Cassie submitted a report to postal inspectors and put the word out in an email to neighbors.

These criminals seem to be going after the wealthier neighborhoods.

Tracking cryptocurrency, like bitcoin, is difficult but it can be done.

Should you receive one of these letters, do not pay the ransom!

Alert postal inspectors and the FBI.