At first, the message seems harmless - an email pops up on your screen that could be from a friend or colleague. 

But click on it and your blood will run cold.
Because what follows is a string of vicious threats to destroy your life unless you hand over money.

The 'ransom' email explains that you have been caught viewing an adult website - captured on your computer's camera.

To add credibility to the sting, the email includes key private details, such as your phone number and secret passwords for a bank or shopping account.

The effect is chilling, as Sarah Hartley, a Mail on Sunday journalist, found out for herself when she was targeted recently. 

'Like most journalists, I am as tough as old boots and used to dealing with all sorts.

Yet what horrified me most about receiving such an email is that it breached my work firewall,' she says.

'That was my fault - the email name had looked credible. It came from a common female name and I had assumed it was a public relations adviser.
So I clicked on the option to permit.

'But when I read it I flushed hot and cold from head to toe - I was stunned by the sheer nastiness of the words.

[see below]. 

'If the person had been standing in front of me I felt they would have been wielding a knife. Adding to my sense of fear was that the email included a password I use for an online shopping account. A barrier had been broken.'

Hartley adds: 'Although I knew I had not been watching pornography, the way I was threatened - that a video of me would be passed on to contacts if I dared breathe a word - was horribly menacing.

'I would have been mortified to know my friends and work colleagues might be contacted in this way.

The language was perfect - no hieroglyphics or request to send money to a Nigerian bank account - and that is what made it plausible.'