Ghost Sec, a group of hackers associated with Anonymous, have reportedly replaced an Islamic State propaganda site with an ad for Prozac.
The militant group's website, Isdarat, appeared on the so called dark web which is only accessible using specialised software.
Ghost Sec reportedly targeted the site with a message telling ISIS supporters to "enhance your calm."
According to the International Business Times, the hacktivists spotted Isdarat on the Tor anonymity network , which is a group of volunteer-operated servers that provide users with a highly secure and private connection.
The replacement message 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."
It accompanied an advert for an online pharmacy that sells medication including Viagra and Prozac.
Anonymous declared war against ISIS following attacks in Paris that left at least 130 dead.
Their strategy so far has included unveiling social media accounts linked to ISIS as well as Rickrolling a selection of Twitter profiles.
However, they have come under fire in the last few days as their "hit-list" has included names and profiles of innocent people who have never supported ISIS.