The FBI's Jacksonville division warned central Florida residents and others of a blackmail scam claiming to have evidence of adultery to its victims. The scammer usually threatens to reveal the information to the recipient's family or spouse unless demands are met, according to the FBI.

The warning issued on Monday says the scam begins when the scammer sends an anonymous letter claiming to have uncovered evidence that the recipient of the letter has committed acts of adultery.

The scammer then threatens to reveal the evidence to the victim's family, friends or spouse. To avoid detection, the scammer often insists on being paid in Bitcoin, a virtual currency, the FBI said.

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CBS affiliate WLTX obtained one of the letters in the blackmail scam. The scammer writes to the victim: "I know about the secret you're keeping from you wife and everyone else. I have evidence of what you've been hiding."

This blackmail scam isn't new, although the FBI says it continues to evolve as scammers change tactics. The FBI warns it's unknown how widespread this version of the blackmail scam is currently but a similarly worded letter has been reported to law enforcement agencies "across the country."

If you come across this scam, FBI recommends you report it to law enforcement. You could also submit information to the FBI's Internet Crime Complaint Center.

The warning comes as a study released in June reveals sweepstakes, lottery and prize-related scams cost Americans millions of dollars each year. The Better Business Bureau calls these schemes some of the "most serious and pervasive frauds operating today."