A Pakistani policeman checks a commuter at a security check point in Peshawar following the killing of Taliban leader Hakimullah Mehsud in a US drone attack in the Pakistan tribal region.
It began innocuously enough - two men on a motorbike delivered a plain brown envelope to the home of Mohammed, an Islamabad businessman. But the contents plunged him into a terrifying three-month nightmare.
The letter, headed with the banner of the Pakistani Taliban, informed Mohammed that a Taliban judge had found him guilty of not living by Islamic principles.
It said Mohammed - not his real name - had been fined five million rupees ($50,000) and threatened dire consequences if he went to the police or failed to pay up.
"Our squad of suicide bombers is always prepared to send non-believers to hell, God willing," the letter seen by AFP read.
At the bottom, the name of feared Tehreek-e-Taliban Pakistan (TTP) chief Hakimullah Mehsud was written in bold followed by a signature that resembled his name.
Mohammed had no way of knowing it, but the signature was fake.
He had been snared by criminals exploiting the terrifying reputation of the Pakistani Taliban to extort money from rich businessmen in Islamabad and its twin city Rawalpindi.
The Rawalpindi chamber of commerce says its members regularly receive extortion demands of up to $100,000, and last month a property dealer in the city who refused to pay a demand found explosives hanging from the door of his office.
The leafy capital, home to foreign embassies, international aid organisations and well-to-do officials, has remained relatively peaceful in recent years as attacks by homegrown Islamist militants have rattled other parts of the country.
But fear of the TTP, which has killed thousands of people in a bloody campaign against the state over the past six years, runs deep and criminals are cashing in.
Multiple sources in the security agencies and among the militants confirmed that the signature on the letter sent to Mohammed was fake and did not resemble that of Mehsud in any way.
Mehsud has since been killed in a US drone strike, but at the time, his name alone was enough to strike terror into Mohammed.
"I was scared to death when I read the letter. It was the most frightening experience of my life -- I didn't know what to do," Mohammed told AFP.
"I avoided going out of the house and didn't even go to work. I was also worried about my family's safety, my kids going to school."
He shared the letter with his wife but even then they were too afraid to go to the police.
"She said the Taliban were also attacking the police and intelligence agencies, they can't protect us from them," he said.
The letter gave a phone number and time to call, and the man who answered spoke with a Pashtun accent - the main language of the northwest, where the Taliban have strongholds.
There followed a series of calls from strange numbers which he later came to know were from Waziristan, in the tribal areas where the Tailban have hideouts, and Afghanistan.
It took three months for Mohammed to resolve the situation, but he refused to say how he paid the money.
Over the past two years at least four businessmen are thought to have been killed by militants for not paying ransom demands, and a senior intelligence official told AFP it was natural victims would take threats seriously.
"Posing as member of the Pakistani Taliban is the easiest thing because the victims then get the impression that they are dealing with a very mighty thing," a senior intelligence official told AFP.
"So they don't report the case with the police and are very ready to cooperate with the criminals."
Islamabad police say 17 extortion cases have been reported this year - compared with none last year - but there could be many others that go unreported because the victims are too afraid to go to the authorities.
The situation has become so severe that the TTP were recently forced to issue a statement denouncing extortion attempts.
"Threats are being hurled out and money being extorted from rich people in all big cities including Peshawar in the name of Tehreek-e-Taliban," said the statement posted on the TTP media arm's website.
"We consider wealth of a Muslim as sacred as his life and announce our disassociation from such acts."
'Help pay for jihad'
Not all of the letters are directly threatening in tone.
One sent to an Islamabad lawyer appealed to his religious conscience to help fund the militants' struggle, saying it cost $30,000 a day to feed their fighters.
"We cover our expenses with the help of God-fearing Muslims like you. Allah has provided you the opportunity to put your effort in the jihad and serve him and his fighters," the letter said.
"You are instructed to arrange for the food expenses of the lions of Allah for two days."
The handwritten letter was again signed with Mehsud's name, but follow-up calls and letters put police on the trail of the culprits.
"The extortionists knew everything about the lawyer, his family, the number of his kids and when he leaves for and comes from the office," a police officer on the case told AFP.
"This was the biggest clue and we investigated and found that the extortionists were actually labourers who were working in the lawyer's home."
The lawyer admits he was lucky - the police rarely catch the extortionists, leaving businessmen to pay up, and in some cases they are even in on the racket.
Islamabad police spokesman Mohammed Naeem said 13 people had been arrested over extortion - including serving officers.