It began with a warning -- Telegram groups notorious for sharing illicit sexual content had set their sights on student Stasa Ivkovic.
The groups were searching for intimate photos of Ivkovic and trying to track down her personal information, according to an anonymous tip she received in 2021.
"They found out everything -- my address, who my parents are, and all my other personal information," the founder of the Belgrade-based rights group Osnazene -- or "Empowered Women" -- told AFP.
Then came a daily deluge of vulgar and insulting messages and comments on her social media accounts.
The episode sparked Ivkovic's years-long descent into the dark corners of social media chat groups in Serbia, where members regularly share revenge porn, child pornography and other unlawful images.
Ivkovic and two other women from Osnazene were able to infiltrate multiple Telegram groups and later exposed the methods used to share, purchase and request illegal content.
Osnazene published their findings in a report in June, claiming that an estimated 10,000 messages are sent daily on the groups they monitored in Serbia -- with one of the largest having up to 70,000 members.
According to Ivkovic, members frequently use codes like "teen trade" or "-18" to search for child pornography.
Even more shockingly, "male family members, mostly sons, take pictures of their mothers and sisters and then send them to these groups for rating, sharing, and various other purposes," Ivkovic said.
Images shared online also include upskirting pictures, photographs taken under women's skirts on public transport.
"Women are literally not safe anywhere," Ivkovic told AFP.
In one harrowing case, a video of a rape was shared in one Telegram group, with the victim only learning about its existence after it was circulated on numerous chats.
The video later appeared on a pornographic website but was quickly removed.
Serbia's Commissioner for Protection of Equality attributed the rise of the groups in the Balkan nation to "deep-rooted, traditional, patriarchal stereotypes about gender roles in families and communities, where women are seen as the property of men."
The findings come as Telegram has come under greater scrutiny after the arrest of founder Pavel Durov in France last month.
Durov has been charged with several counts of failing to curb extremist and illegal content on the popular messaging app.
Telegram has positioned itself as a "neutral" alternative to US-owned platforms, which have been criticised for their commercial exploitation of users' personal data.
But opponents of Telegram have regularly accused it of providing a digital marketplace where users can share extreme sexual imagery, disinformation and traffic drugs.
Serbia has a chequered history with encrypted apps.
A vast FBI-led sting operation in 2021 targeting the Sky ECC app led to the arrest of a leading figure from the Serbian underworld, after accounts linked to the suspect posted pictures of gang members dismembering corpses near the capital Belgrade.
The rapid growth of illicit social media groups has been a persistent issue in Serbia in recent years.
Serbia's Special Prosecutor's Office for High Tech Crimes did not respond to AFP enquiries about ongoing investigations against chat groups.
Authorities, however, have been slow to act, with just 13 groups shut down by officials, according to a report in a local investigative outlet.
Activists like Ivkovic say the problem is only worsening in the face of government passivity.
Unlike in neighbouring Montenegro and Croatia, Serbia lacks specific laws on the sharing of unauthorised recordings and distribution of pornographic content, including revenge porn.
Legal expert Jelena Drndarski said that while suspects in possession of child pornography can be prosecuted, victims of revenge porn have to take a civil case against the perpetrators, who are difficult to track because they use anonymous profiles on platforms like Telegram.
From early 2011 to mid-April 2024, 717 people were charged with possessing child pornography and exploiting minors, but only 408 were convicted -- most being given fines and suspended sentences.
Belgrade's Autonomous Women's Centre (AZC) has called for tougher laws against the sharing of unauthorised and illicit content, with a petition signed by tens of thousands of people.
But even with new laws, life for the victims can be grim, according to AZC's Vanja Macanovic.
"These videos and photos remain online forever, and the victims live in fear that someone will see them again, potentially restarting the cycle of violence," said Macanovic.
