An ISIS propaganda website on the dark web has been hacked and replaced with an advert for a service selling prozac and viagra tablets which told extremists to 'calm down.'

The site for the terror group appeared on the Tor browser of the dark web last week in a bid to get extremists to join up.

However, less than a week later, the site had been hacked and visitors to the page were greeted with a message for the medication.

It read: 'Too much ISIS. Enhance your calm. Too many people are into this ISIS-stuff. Please gaze upon this lovely ad so we can upgrade our infrastructure to give you ISIS content you all so desperately crave.'

According to the IBT, the website was taken down by Ghost Security Group, an independent counter-terrorism network.

It is believed to be the first time that a hacking group have taken down a website on the dark web.

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The dark web is a subsection of the deep web - the part of the internet that does not show up in searches or on social media.

Most of the information on the web is far down on dynamically generated sites, unable to be found or seen by traditional search engines.

The dark web is used as a way of sharing information and trading goods, but the anonymous and encrypted nature of it has attracted large amounts of illegal activity.

Earlier this week, Ghost Security Group said that they had members posing a would-be jihadis in order to infiltrate sites on the dark web.

The group's executive director, who declines to be named, said: 'We're playing more of an intelligence role.

'The group is a volunteer organization that has been sending data to the FBI and other agencies via a Congressional terrorism adviser, Michael S. Smith II.'

Meanwhile, fellow hacking group Anonymous has promised to hunt down militant jihadists online following the terrorist attacks in Paris last week which left 130 people dead.

Anonymous' declaration of war came in a video posted on the group's French YouTube page shortly after the Paris attacks, where they warned the terror group to 'expect us', vowing to hunt down those responsible online and expose them.

Wearing the group's signature Guy Fawkes mask, a spokesman says in French: 'Anonymous from all over the world will hunt you down.

'You should know that we will find you and we will not let you go. We will launch the biggest operation ever against you. Expect massive cyber attacks. War is declared. Get prepared.'