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MAINZ, Germany — Dozens of people who visited Switzerland's largest strip club have received letters threatening to expose them and "destroy" their lives unless they pay a ransom of more than $2,000 in bitcoin.

Between 50 and 60 patrons of the Globe in Schwerzenbach, near Zurich, received the threats to send pictures to their family and friends, nightclub manager Fritz Mueller told NBC News late Tuesday.

According to a copy of the letter posted by Swiss TV channel Tele Zueri, it said the sender "knows who you are and what you did" and demanded the equivalent of more than $2,000 in the crypto-currency bitcoin to be paid within 5 days.

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"We are moralists and you are our target," read the letter dated Feb. 17. "We hope that you are not suffering from amnesia, otherwise we need to jog your memory with a few photos."

The letter ended: "We will destroy your life, the way you do it with others."

Mueller said the sender may have learned the identities of people attending his club because it is possible to request the names of Swiss vehicle owners using license plates.

The club has beefed up security, but Mueller believes the photographs from inside the club may not actually exist because cameras and mobile phones are not allowed in the building.

The prosecutor’s office in Zurich confirmed to NBC News that criminal complaints from "several affected people" were being investigated by investigators.

Swiss media reported this week that customers of several other clubs also received similar letters.