Scammers have sent blackmail letters threatening to peddle false rumours that people are paedophiles unless they hand over money, police have warned.
The menacing letters warn they will subject families to a "smear campaign" and force people from their homes unless they deposit bitcoins - a type of cyber currency - into a specific account.
And in a chilling warning, they say anyone who dares to tell the police about the threats will "go through hell".
Eleven people across the affluent Thames Valley area have received the alarming letters, and officers believe the cases may be linked.
The letter warns those who have received it that they have been "selected carefully".
It goes on to state: "If you do not follow these instructions to the letter you and your family will be subjected to a campaign that will include writing to your neighbours informing them of your love for young boys.
"We will spread this rumour at your local school which will result in you, your family and your home becoming the target for attacks and vandalism.
"Whether the rumours are true or not does not matter in the slightest. You know what people will think once we put the ideas in their heads? No smoke without fire is what they will think."
And they warn the only way to avoid the campaign of intimidation is to pay two bitcoins into a specific account.
It adds: "If you tell anyone else about this letter or its contents, for example the police then we will go ahead with the action and your family will go through hell."
And in a menacing footnote it states: "The clock is ticking, you have 72 hours."
Eleven people have reported letters like this to the police in Maidenhead, Wycombe, Hedgerley and Bourne End, Thames Valley Police said.
Det Sgt Peter Wall from Force CID Maidenhead urged anyone sent one of the letters to contact police.
He said: "Do not be alarmed if you receive a letter like this. Our advice is to try not to touch the letter too much so that it can be preserved for forensic examination and then call 101. Do not respond to the letter or purchase any of the bitcoins.
"Some people may simply discard letters like this when they receive them but for others it can be very distressing.
"This is a clear attempt at blackmail and we need to gather all the information we can to aid our investigation and trace the offenders behind these nasty letters."
Anyone with information should contact Thames Valley Police on 101 or Crimestoppers anonymously on 0800 555 111 or online at Crimestoppers-uk.org.