Bieber is Twitter’s biggest attraction, boasting the most followers in the world. The hashtag is used hundreds, if not thousands of times an hour, and rockets to tens of thousands of times when the star is trending.
The star’s fans are called Beliebers and many of them are under ten years old.
ISIS – also known as Daesh – recently uploaded one of its propaganda films to a different site and included the international pop star’s #JustinBieber hashtag.
This means youngsters looking for news about the diminutive star would be shown a link featuring a sickening video by ISIS preaching death and hatred to the West.
The video features a bearded man speaking English with what appears to be a British accent and depicts scenes of fierce battles and rotting bodies covered in flies.
One mother, who asked not to be named, said she was “appalled” that nine-year-old children like her daughter could stumble across the video while looking for Bieber fan photographs.
The 40-year-old mother who lives in Epsom, Surrey, said: “I do let my daughter use Twitter and she knows all about using hashtags to search for Justin Bieber news and pictures.
“I would be horrified if she ever saw images such as those in the video.
“Many of Bieber’s fans are so young and to target children in this way is typically horrific of ISIS.
“I will certainly think twice about letting her loose on Twitter now.”
ISIS is well known for using social media platforms to spread its warped messages and horrific videos of beheadings and other savage executions.
Dozens of disaffected youths have also left their families behind in the UK and fled to Syria after being lured to the terror group’s de facto capital of Raqqa after being groomed on Twitter.