She yelled to her parents that she was being "hacked" and tried to remove the explicit photo.

Her father, Wayne, promptly reported the incident to police, but weeks later, he remains furious that his daughter was exposed to the image.

"We lock our doors and our windows to protect our children, but these predators are getting in through our computer screens. It's very alarming."

Roblox, a popular game among children and teens, with 1.7 million users, allows users to build and share video games.

Another user may have sent Phoebe the image, or embedded it in the game she was playing.

Roblox is among a slew of popular games and apps – some of which are being taught in Victorian classrooms – which Victoria Police has warned are being used by predators to groom vulnerable children.

Victoria Police is fielding a rising number of complaints about the computer programs which allow users to interact, including Roblox, Minecraft and Musical.ly.

Detective Senior Sergeant Boris Buick of the Joint Anti-Child Exploitation Team said: "Police are extremely concerned that commercial applications are increasingly used by child-sex perpetrators to seek to contact and groom children."

Musical.ly is a video social-networking app which includes live broadcasting and has been described by cyber-safety expert Susan McLean as akin to "taking a photo of your child and handing it out at the local park".

Yet the app is being used in at least one classroom after a teacher signed up her entire class, said Ms McLean.

Minecraft, one of the most popular games for kids and teens, allows users to build virtual worlds.

It is used in almost every classroom to teach students how to use code.

Schools usually apply a controlled classroom setting to the game, making it safe for students.

But Ms McLean, who works with schools across the country, said the approach to cyber safety was inconsistent.

While some schools blocked students' access to unauthorised sites and monitored their online activity, others had few protections in place.

"I think a lot of schools still don't quite understand the reality of online risks," she said.

Ms McLean said she was not aware of schools using Roblox.

The Office of the eSafety Commissioner said it conducted 338 investigations into children's cyber safety two weeks ago – the highest number of investigations completed in a single week this year.

The office is warning that students are being groomed to share naked images of themselves, which are then being downloaded on the dark web by predators.

Commissioner Julie Inman Grant said her office has launched a new checklist for schools to help them form robust online safety policies.

"Generally, apps that allow photo or video sharing or have messaging capability tend to be the most concerning to parents and schools, particularly those messaging apps that can be taken offline and facilitate interactions with strangers."

IT teacher Roland Gesthuizen, who regularly taught Minecraft to students (but did not use Roblox due to its lack of classroom controls) said he always used a protected school server when students played the game.

"Teachers who use this technology have to play with it and understand the implications of creating an account and the interactivity with anyone who might be from outside the school," he said.

"Safety is first and foremost."

Victorian education department spokesman Alex Munro said a new online portal is helping schools beef up their cyber safety.

"Victorian government schools have access to a world-class IT system, backed by top-of-the-line internet filtering and layered security to keep students safe while online," he said.

A Roblox spokesman said the game was expanding its moderation team to more aggressively delete content and include parental controls, enabling them to shut off the game's chat capability.

"We want all users to be safe on Roblox and we will continue to invest in the safety of the game," he said.

A spokesperson for Microsoft, which owns Minecraft, said parents were able to change communication and sharing settings on the game to protect children. 

Musical.ly did not respond to questions.

Tips from the eSafety Commissioner on how you can protect your children online:

The Age