“Hi Hannah Mossman Moore

Stalking you has its benefits. Now watching your friend strip another blonde with perky tits. She’s not more than 22. I have seen your tits so many times in the recording. You are late 20s now? Declining youth and saggy boobs… There is so much to learn when one just follows you around. Have you left Sri Lanka or just hiding from me? Tell me please. I will come and get you.

Ciao”

Hannah was 23, not long out of university, and had just landed her dream job. She was an intern with a new jewellery brand called Alighieri, and although she was being paid little more than expenses, she had been thrown into the deep end and was loving it, not least because she got to go to London fashion week.

“It had always been my dream to go,” she says. And now she was there “as a professional”, as she puts it. It felt like her first big break. She was the company’s first employee and was given the task of hanging out in the “designer showrooms”, London fashion week’s marketplace – a melting pot of teenage models, fashion insiders and hangers-on. Her job was to try to find the elusive white whale that every new brand was desperately chasing: buyers.

The golden goose was a cash-rich foreign buyer. And as luck would have it, Hannah found one. Or maybe not luck. Although Hannah was young and in a new environment, she is also a natural extrovert: sunny, open, chatty. She’d bumped into an acquaintance, the friend of a friend, and he introduced her to his friend: a well-groomed Hong Kong national called Kin Hung.

“It was just a huge relief,” she says, “to have proved myself.” Kin seemed to be the real deal, a big wheel with major contacts in the Asian fashion market.

They posed for a selfie together and Hannah gave Kin her contact details. And that was where it all began. Though for the longest time, Hannah wasn’t sure what “it” was. Kin had VIP passes and could get into any show, magic up tables at any restaurant. For two years, he was her friend and “mentor”. Later, without even realising how it happened, Hannah slowly found herself in a bizarre constructed reality – a fly in a spider’s web of false narratives.

The short version of the story is that for much of her 20s, Hannah had a stalker. Or maybe stalkers. Someone who’d gathered information on her – photos, details of her private life, jobs, family, locations – and bombarded her with abuse, threats and worse. Someone who watched her and hacked her bank account and her phone account. Her mobile phone was repeatedly cut off: she’d find herself somewhere and not be able to get home, not able to call anyone. It happened not just once but seven, or eight times.

And not just her phone: her dad’s was targeted too. A photo of her mother’s front door was emailed to her, legal threats were sent to her brother’s home, new email accounts in her name were set up to impersonate her. One of these, “Premium Escorts”, purported to be selling her sexual services. She was threatened with lawsuits and criminal action. WhatsApp groups were created by a fake Hannah in which she confessed criminal activity to friends and family. She also received threats of violence and rape.

At first, she tried to deal with it alone. Eventually, she went to the police, handing over folders of evidence, pages and pages of printouts. When they finally took action, they went to arrest a suspect, found he wasn’t home and gave up. Later, the police wrote to Hannah and told her they’d closed the case. “Evidential difficulties,” they said. The stalking continued.

* * *

It’s now a decade on; Hannah is older and only just starting to understand what happened to her, not least because her story is now a 10-part BBC podcast, Stalked. What seems even more unbelievable, as I write these words, is that I knew Hannah all the while this was going on. To some degree, the podcast is my way of making amends.

We set out to do what the police failed to even try to do: solve the crime. And thanks to the tenacity of Stalked’s producers, Georgia Catt and Rob Byrne, we believe we are nearer to solving it. The motivation for doing so, at least in my case, is because of the guilt of not realising what was going on underneath my nose, even though this whole story was in many ways on my investigative patch.

Hannah, I should explain, is my ex Dave’s daughter, and although we’d split up many years earlier, they’d both remained in my life. We celebrate birthdays and milestones together. Dave is the honorary co-parent of my dog. The three of us share endless silly animal videos in our WhatsApp chat.

At the peak of Hannah’s nightmare, I’d been deep in the throes of my investigation about Cambridge Analytica, Facebook and the weaponisation of social media. I was overwhelmed, wrestling with a massive story and my own frayed nerves and security concerns, unaware that Hannah was dealing with what, in hindsight, seems like a human version of Cambridge Analytica: a malign influence in her life who was harvesting, profiling, surveilling and targeting her.

So much of my work of the past decade has been about Silicon Valley surveillance. It’s the underlying business model of all social media platforms: they track us – even if we’re not on them – to monetise us. The whole thrust of the Cambridge Analytica story was how personal information collected for one purpose – a personality quiz – could be repurposed for another: electing Donald Trump. Yet I was oblivious to how a similar thing was happening to Hannah. How someone had her personal data – lots of it – and was twisting it and weaponising it against her.

It wasn’t until the second lockdown – the dreary, endless, dark, cold winter lockdown that began in England in November 2020 – when I went with Hannah for a long, looping walk around my part of north London, that it finally started to come into focus.

At this point, Hannah was 28, living with her dad and attempting to set up her own jewellery business while hustling to make money: moonlighting as a barista and trying, like we all were, to get through a pandemic without losing her mind. We were walking uphill through my local park when, offhandedly, Hannah mentioned something about “Swami”. I said: “Swami?” – and she sort of shrugged despairingly. “You know, Swami – he was one of the hackers, supposedly. You know, the whole online reputation management thing.”

She was right: I did know about Swami and the hackers and the online reputation management thing. It had happened after a terrifying incident with Kin in Florida in which, two years after Hannah had known him, he’d allegedly become aggressive and controlling and tried to prevent her leaving. His behaviour in person and texts between them show that she was terrified and begged to leave. He claimed that his out-of-character conduct was because he’d been hacked. What happened next was deeply confusing. An entire cast of characters starting communicating with her, multiple different people, all abusive in different ways. Kin claimed these were “the hackers” who had “jumped” to her.

Hannah had a stalker in the way that some people have a health condition; something such as lupus – uncommon, mysterious, little understood. It was a permanent feature of her life that occasionally flared into crisis but which most of the time she tried to ignore, minimise, pretend wasn’t happening. That day, when there was nothing else to do but walk endlessly, I made her stop. “Just go back to the beginning,” I said. “And tell me the whole story.”

What tumbled out in fits and starts over hours was unbelievable. It began with meeting Kin, the charming, helpful man. And somehow gradually escalated into a sophisticated campaign designed to ruin her life. It had, in part, succeeded.

At one point, Hannah pulled out her phone. “Look,” she said. There was email after email of pornographic material. Some were addressed to “Hooker Hani” and fixated on the idea that she was a sex worker “with a body like an over-fucked buffalo”. Some were soliciting reports of the putative clients who’d supposedly used her sexual services. Mixed in were photos of Hannah as a young student. “I don’t even know where those photos are from,” she said. There were details of her life, of her locations. Even while we were talking, another arrived. By the end of the walk, four new ones had landed in her inbox.

In the jumbled relaying of the story, Hannah introduced a new character: Alice. “It’s what also happened to Alice,” she said. “Who’s Alice?” I asked. Was this another harasser? “Alice Ruggles,” she said. Hannah explained that Alice had taken her place at her school in Leicester when Hannah’s mother had accepted a teaching post abroad. “I never knew her but she became best friends with all my best friends.” Alice had a stalker too. “And she’d also tried and tried to get the police to help.” That help never came and she’s no longer around to tell the rest of her story. In 2016, Alice’s stalker murdered her.

* * *

I felt a profound sense of hopelessness when Hannah finally opened up to me. The next weekend, she came around to my flat with bundles of documents. There were at least nine different characters communicating with her and between themselves. It was wildly confusing, the kind of investigation that needed time and focus and a team, and in early 2021 I had none of these. Instead, I had my own issues: a defamation lawsuit that ate my time and, even more so, my spirit.

But what I landed on was an idea. I’d been blown away by a BBC podcast series called The Missing Cryptoqueen. It combined an investigation, public service journalism and vivid storytelling in a way I hadn’t heard before, and Georgia Catt was the producing genius behind it. I emailed her.

She sent an upbeat response, which I forwarded to Hannah, although I worried that I was getting her hopes up. Two weeks later, Hannah called me. “You’re never going to believe this.” What? “It’s stopped!” What’s stopped? “The emails. Everything. It’s all just stopped dead.” A coincidence? Or had someone been in her emails? We still don’t know the answer to that. A relentless campaign that had been going on for four years suddenly went silent.

Stalking is the only crime where victims are meant to obtain evidence for themselves, says Rachel Horman-Brown, a solicitor who specialises in stalking. “If you report a burglary, you don’t have to present fingerprints to the police. It just doesn’t happen for any other crime. And the thing is, stalking nowadays in virtually every case will involve an online element, which means there’s a digital footprint, which means that it is provable. If they want to find out who’s doing it, it’s possible because the evidence is there. They can’t be bothered, in my view.”

Catt and co-producer Byrne systemised all the evidence and then found a team of forensic linguists who work for the FBI and who dusted for metaphorical fingerprints in the copious written materials. It’s the same technique that was used to identify the Unabomber, and Robert Leonard, professor of linguistics at Hofstra University in New York, was able to pull out endless similarities between the apparently different styles of the various messages, suggestive of “evidence of common ownership”, meaning they were written by the same person or persons.

Another data expert, Jonathan Sebire, who works for Premier League clubs identifying and managing threats against footballers, examined the data trail, which revealed a pattern linked to Kin’s movements. A psychologist of stalking, Alan Underwood, assessed the messages and the same driving psychology behind them all: “an intimacy seeker”.

In last week’s episode (number six), after carefully evaluating all the evidence with the BBC’s lawyers, we named the man who we have reasonable grounds to believe is the perpetrator behind it all. The man who the evidence suggests to us is every single one of these characters, who sent the rape threats and is the person behind the Premium Escorts account: Kin Hung. The charming, friendly, helpful man who Hannah met at London fashion week when she was 23. Kin denies this and adamantly denies ever stalking Hannah.

“True crime” has a mixed reputation, muckraking over salacious murders from decades ago, but Stalked is something different. Most victims of stalking and harassment do not receive any sort of help and – only in rare instances – justice. No woman should have to rely on a ragtag team of journalists for answers but that’s where we are.

* * *

Four years on, it no longer seems like such a coincidence that two girls from the same class at the same school would both have stalkers. Or that neither of them had been able to get the help they needed from the police. One in five women will experience stalking, according to the Office for National Statistics, and one in 11 men. It would be more unusual for a single class of schoolgirls to grow up and not to have a stalker. In the vast majority of cases, the perpetrators are never caught: only 6.6% of cases reported to the police in the year ending March 2022 resulted in a charge. Just 1.4% in a conviction.

What we realised while making the podcast is that stalking is an epidemic. It’s mostly invisible. It ruins lives. And it’s rapidly growing, partly because there are now so many tools available to assist a would-be stalker. Most cases of stalking now involve a cyber element, and surveilling, profiling and targeting someone via legal and illegal means is both easy and common.

If it’s happened to you or someone you know, the first thing to realise is that you’re not alone. And the second is that there’s nothing you could have done differently. It’s not your fault. It’s that feeling of blame and shame that took Hannah so long to shake. But there was nothing she could have done.

What I’ve come to understand is that part of the reason I hadn’t realised the extent of what was going on or how badly it affected Hannah is that so much of what was happening to her was private, mediated by technology, targeted directly to her phone. And that Hannah also used technology to mask the truth. During one of the peaks of the malicious activity, she ran away to Los Angeles to stay with a friend, posting photos on her Instagram account of sunsets, cocktails, glasses of green juice.

Hannah always said “my stalker” with ironic air quotes. One of her biggest eye-rolls was towards anyone she felt was acting like a victim. It was – her words – an “ick”. It wasn’t that she was unsympathetic towards others; she just had a horror of being one herself. Hannah dreamed of being an accomplished businesswoman: having her own company, being successful, independent – the exact opposite of a victim.

But Hannah was a victim. It was just something that she’d refused to acknowledge to anybody – especially herself. Even as her life unravelled and she retreated from her friends: “I didn’t know what to say to them,” she said and moved back home with her dad. “I think she’s just relieved to be here,” he told me. She felt “such shame and embarrassment”.

It’s been a long and arduous process to unpick everything. Hannah has had to expose herself, hand over the passwords to her accounts, let Catt and Byrne and the lawyers trawl through her private life. We know Hannah was stalked and “hacked”, whether through technological or social methods. But we have no certainty over who or how. We don’t know whether Kin is behind it all. We do believe, however, Kin is involved; the evidence is too compelling to feel otherwise. He has responded robustly through his London lawyers: Kin denies all accusations and adamantly denies ever stalking or harassing Hannah, rejecting the allegations as “false and without foundation”.

The first use case of all new technology is to weaponise it: to surveil, target, control. An estimated 96% of deepfake video is nonconsensual pornography. A not insignificant percentage of that is directed at children, girls.

Eight years ago, I went with Christopher Wylie, the Cambridge Analytica whistleblower, to an electronics shop in Tottenham Court Road in central London, where in an upstairs room, behind a closed door, we looked at undercover filming equipment. A few months ago, I went back with Georgia and Hannah, and a salesman showed us his current range of products, which had advanced beyond recognition: spyware in all shapes and forms – all of it legal to buy.

A simple white phone charger, identical to any number you’ll find in your own home, was the one that I found myself marvelling at. It turned out to be a voice-activated recorder. When a conversation starts, it records, and when it ends, it automatically messages you a sound file. Technology that was once the preserve of nation states is now available to anyone for a few pounds.

And then there’s your personal data. Silicon Valley is itself a surveillance tool. It’s what its entire economy is built on. Your personally identifiable data has been vacuumed up by shady middlemen. It’s more difficult here, but in the US, private investigators use it to deliver detailed and incredibly intrusive intelligence reports in a matter of minutes.

Regardless of the who and the why of it all, the effects on Hannah were profound. We laugh now about the list of numbers that I have for Hannah in my phone: Hannah – Android, Hannah – New 2017, Hannah LA, Hannah New Moby, Hannah New Number, Hannah – New 2018, Hannah (new) 2019, Hannah USA…

But it’s a record of a woman being hunted, in flight. For a period, she didn’t have any phone at all.

Making the podcast – being listened to and believed, having the support and opinion of experts – has been a life-changing experience for Hannah. She’s regained control of her life, her narrative. It’s been a huge privilege to see, and we’re both acutely conscious of how most women don’t have that opportunity. The most affecting moment in the series is when Hannah goes to meet Alice Ruggles’s parents. It’s so profoundly sad. Alice’s calls to the police were released, and her polite, don’t-want-to-make-a-fuss tone is the hardest thing to hear. “I know this sounds crazy,” Hannah tells Sue, Alice’s mother, “but I never wanted to inconvenience him.” Sue replies: “That’s exactly what Alice said. Exactly the same.”

The Metropolitan police asked Hannah for a meeting last month and apologised to her for the handling of her case. Mistakes were made, they said. They no longer issue “first harassment warnings”, which have been widely accepted to be valueless. In a statement, Commander Kevin Southworth said: “We recognise the service the victim received between 2018 and 2020 fell short of what is expected… Since 2022, we have significantly improved our response to stalking and in the last year have investigated more cases of this nature than ever before.”

I learned things, too, through the making of the podcast. It had never occurred to me that there was any overlap between Hannah’s experience and my own. Hannah’s privacy and peace of mind had been relentlessly shredded. She’d been targeted and abused in private: a torrent of messages, threats, intimidation and confusion sent direct to her phone. She’d been sexually shamed and exposed. She’d retreated into herself and isolated herself from friends and family. She felt despair and hopelessness.

The thing is that I could have written that list about myself. Observer readers may know something of the very public online abuse I received through the years of my Brexit investigation.

Hannah was shamed for being young, attractive, sexually desirable. She was a slut – “Hooker Hani”. “Her vagina has more STDs than a toilet bowl has germs,” the perpetrator wrote to her then boyfriend. I was shamed for being the opposite: older, childless, a “mad cat woman”, or what, in previous centuries, used to be called a witch.

It’s a measure of how effective these strategies are that although Hannah and I are very close, neither of us knew at the time what the other was going through. So much is internalised. The silencing is real.

The first victims of all new technology are women. But they’re never the last. If you want to understand what’s coming down the line in the future, you need to look at what’s already happening to women now. This use of technology to surveil, target, shame, bully, coercively control; it’s the same technology that is now being deployed by Trump and, especially, Elon Musk against people they consider enemies. Musk more than anyone understands that data is power. We’re all prey now.

• The first five episodes of Stalked are available on BBC Sounds