Optus has apologised after a stalker in Melbourne's northern suburbs repeatedly tricked the telecommunications giant into giving her the phone numbers and account login details for one of her victims.

You can read our in-depth story to find out how Lydia Abdelmalek used the identity of Australian actor Lincoln Lewis to relentlessly stalk and harass two women.

Here's how she duped one of Australia's biggest telecommunications providers into helping her do it.

The conversation appears innocent enough.

An Optus customer has forgotten their new phone number, so they go online to ask an assistant, Ringgo, for help.

RINGGO: Hi there! Welcome to Optus Live Chat! How can I help you today? VISITOR: Hi Ringgo. RINGGO: How are you? VISITOR: I'm great thanks, yourself? If I give you my old mobile number can you give me my new service number?

Optus asks three basic security questions: name, date of birth, phone number.

It's supposed to confirm the person's identity and screen any fraudsters.

But there's a problem.

The person asking for help is actually an imposter who has been stalking their victim, Jess*, for over two years.

Abdelmalek sent several images of Lincoln Lewis to her victim. ( Supplied: Heidlelberg Magistrates' Court )

Jess has changed her number to block the harassment.

But it doesn't work.

The Optus staff member is duped into handing over the new number.

VISITOR: I disconnected that number on the 8th of Feb 2014 VISITOR: And Optus are telling me it's still active, so I just want to know what my new number is? RINGGO: This is the new number 0421 xxx xxx*

The stalker, now ready to recommence the abuse, is still not satisfied.

They also want control of the victim's online account.

VISITOR: Can you help me access my "my account"? VISITOR: I don't know my username or password or the email I have to reset my password RINGGO: Is this the email that you are still using xxx@xxx.xxx? VISITOR: I might not have access to that at the moment, can you send me a temp password to my boyfriend's account?

Ringgo agrees.

He sends new login details to an email that's not even linked to the account.

The stalker now has the victim's new address and other personal details.

VISITOR: Ringgo, you are fantastic!!

TV heartthrob used to lure victim

In 2014, Jess was getting hardly any sleep.

Someone was making a series of harassing phone calls to her mobile, sometimes as many as 40 or 50 a day, late into the night.

They were also sending threatening messages.

"Watch your back," one message said. "Your time is coming," said another.

Jess had changed her Optus account details to stop the attack.

But it was proving futile.

TEXT MESSAGE: Hahahahahahaha blocked you motherf***er … Only took you a second to reactivate your account and I got it done. F*** you.

Jess's harassment started after she met Australian actor Lincoln Lewis aboard a flight in 2009.

The two had shared some friendly banter, so the single mother sent a friend request to what she thought was Lewis's Facebook account.

Years later, Jess sparked up a flirty friendship, seemingly with the soap star, through that account.

The pair went on to talk on social media, on the phone, and even Skype.

Intimate photos were shared.

Revealing photos purporting to be Lincoln Lewis were sent to victims. ( Supplied: Heidelberg Magistrates' Court )

Eventually, a stack of lies led Jess to realise she had been conned.

She had not been talking to Lewis at all.

"They preyed on me being a single parent and being alone," she would tell the Heidelberg Magistrates' Court years later.

Lydia Abdelmalek, 29, was last week found guilty of six stalking charges, after she used the identities of celebrities to deceive and harass people she met online.

'I would never hurt you'

Jess was one of several victims who gave evidence during a three-week hearing.

She told the court that, with the help of Queensland detectives, she had started to record telephone conversations to expose the catfish.

"There's just so much I don't know about you," she said in one recording.

"I just want to be with you and talk and get to know you."

Lydia Abdelmalek's own online accounts revealed nothing of her double life. ( Facebook: Lydia Abdelmalek )

She pretended to forgive the stalker and even convinced them to send money, to create a paper trail.

"Thank you so much for doing that, you didn't have to do that," Jess said.

The stalker offered some reassurance: "I would never hurt you."

It was a lie.

In the background, Abdelmalek was using anonymous accounts to harass and abuse Jess.

EMAIL: Changing your display picture to your useless f***er of a dad and bastard daughter won't make a difference to us we can still find you. PS: your ex boyfriend has been hacked too your nudie skype pictures are now in our possession look out.

The threats extended to Jess's young daughter.

FACEBOOK: Send Charlotte* our love or maybe we might just visit her at her new school next week

Jess could not handle it any more.

Her mental health was plummeting.

Jess changed her phone number, put the account under her father's name and secured it with a pin code.

Initially, it seemed to work.

The phone fell silent.

But, behind the scenes, Abdelmalek was using the Optus Live Chat service to track her victim.

VISITOR: Can I get my password reset link sent to my boyfriends email please? Cause I can't access mine at the moment? MICHELLE: Sure!

Each time Jess changed her number, her stalker found her.

Again.

And again.

The hacker used the online service to glean information about her victim and, eventually, hack the account.

Sometimes the assistant forgot to ask for a pin.

On another occasion, they failed to realise the date of birth provided was incorrect.

VISITOR: I want my mobile number LIA: Just checking on our system what happened on the service. VISITOR: Thanks LIA: Did you requested the service to be transferred to someone else? VISITOR: To my mum or dad maybe? LIA: At the moment is it showing under John* VISITOR: So it's under my dad's name LIA: Yes that is correct LIA: The mobile number is 0403 xxx xxx*

Police traced Abdelmalek's IP address to repeated attempts to get account details from Optus.

Jess told the Heidelberg Magistrates' Court she changed her phone number about six or seven times.

Sometimes she had barely left the Optus shop when she would be informed someone was trying to hack her account.

"This became a daily thing as I tried to stay one step ahead of them," Jess told the court.

"I had to take time off work."

Optus apologises for giving information to stalker

It was only when she finally got her hands on the Optus Live Chat transcripts that it was revealed how the stalker had managed to track her down.

In a statement, Optus said "human error" was to blame for Jess's information being handed to her stalker.

"This information was inadvertently shared due to a human error when the perpetrator undertook a persistent program to fraudulently access the customer's information," a spokesperson said.

"We apologise for our customer's experience."

The company said it has "ceased high-risk transactions" within its Live Chat platform, including changes to email addresses and sim swaps.

According to the company, new security measures were introduced in 2015, including extra fraud awareness training for staff, and compliance audits for frontline staff.

Do you know more about this story? Email vicindepth@abc.net.au

*Names and some details have been changed to protect victims.

*Photos and transcripts are drawn from the case of Jess and were tendered as evidence to the Heidelberg Magistrates' Court.