Some pizza places have received printed letters stating that if they do not pay one bitcoin within a month they would receive a significant number of negative online reviews, and also their pizzas would be contaminated with Mercury, which can be toxic to humans.
The letter also states: "Because many of the actions we take are catastrophic and irreversible, it is advised (to) pay ... before the deadline is reached."
If the restaurants do not pay up a single bitcoin, worth around £339 ($580), then the ransom would be increased to three bitcoins, worth £1017 ($1730).
Some pizza restaurant owners decided to post the letter up on social networking website Reddit, and users suggested that it might be possible to trace the sender by using a technique that finds the make and model of the printer that the letters were created with.
A pizza restaurant owner in Michigan told Sky News he would not pay up: "At first, I'm looking at it and I'm thinking, Oh, it’s one of my friends playing a joke on me.
"There are food costs and finance, labour and the rising cost of gas. Do you really need to have somebody now threatening you with extortion?
"They’re taking your lunch money and we’re not going to let them."
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