The job advert seemed timely. It offered between £500-£1,000 a week to work from home as an agent for cryptocurrency transactions. Lauren*, 21, was heavily in debt after a period of unpaid sick leave and leapt at the chance to rebalance her finances.

“It had been promoted on social media by a couple of people I’d been at school with so I trusted it,” she says. “It seemed such a coincidence that this came along just when I needed it.”

Lauren contacted the recruiter and was asked to provide photos of her passport plus her address and bank details as ID. “They made out that they were verifying me,” she says. She was instructed to open a cryptocurrency account and two savings accounts with her building society, Nationwide, and was told that she would receive commission for handling money transfers.

Her suspicions were aroused when £700 was deposited into her Nationwide current account and she was ordered to transfer it to the new cryptocurrency account. “I was querying this and was told not to ask questions and warned that they had all my sensitive information,” she says. “That’s when my heart dropped.”

Lauren had unwittingly signed up to become a money mule, a person who allows their bank account to become a conduit for the proceeds of organised crime. Online fraud has risen by a third since the start of the pandemic with £2.3bn lost by consumers and criminal gangs are increasingly targeting cash-strapped young people with a clean record to help them move stolen money undetected by banks and authorities. The number of people under 30 suspected of being money mules has soared by nearly 80% in the past year according to figures from the crime prevention agency Cifas – and with university terms starting, students are likely to be targeted with seductive job ads on social media.

The cost for those who sign up can be devastating. While the criminal gangs are shadowy figures, often based abroad, their mules are easily identifiable. Banks are required to question uncharacteristic payments and, if a transaction is deemed suspicious, the account may be frozen and the authorities alerted. Customers found to have used their accounts knowingly or otherwise for money laundering are logged on the National Fraud Database which prevents them from opening a bank account, applying for a loan or even a mobile phone contract. They also face up to 14 years in prison.

Lauren’s accounts were frozen by Nationwide as soon as the £700 was paid in. “The [perpetrators] told me not to admit to anything because I’d be arrested,” she says. “They put everything on to me so I pretended that I knew nothing about the transfer when Nationwide questioned me. It was so scary. I didn’t know who these people were, how many of them there were or whether they lived locally.”

There followed six weeks of fear while Nationwide investigated. Lauren had to have her wages paid to her boyfriend until she was able to open a basic account with another bank. “It was the worst month of my life,” she says. “There wasn’t a moment when I wasn’t thinking about it but I couldn’t tell anyone what had happened. I was so ashamed and alone. I couldn’t eat or sleep. It was difficult to function. I knew I had to be honest but I didn’t know when the time would be right to speak up or if the gang would come for me when I did.”

Eventually Lauren broke down and confessed to a Nationwide fraud investigator. “I was shocked to find that they already knew what had happened. They were just waiting for me to come clean,” she says. “They told me that they dealt with five or six such cases every day and that if I hadn’t admitted everything they would have reported me to the police.”

Not all money mules are lured by the promise of earning money. Charlie*, an international student from Hong Kong, lost her bank account and her creditworthiness in her first term at university after agreeing to do a favour for a new friend.

“She was an Indian national and asked me if her dad could send her maintenance money to me from India as she had not yet managed to set up a UK bank account,” she says. “I agreed and a small sum was transferred to my Lloyds account and I cashed it at an ATM and handed it over. Two weeks later she asked if I could help out again and her dad transferred £1,400 which I also cashed for her.”

Shortly afterwards, Charlie’s account was frozen by Lloyds, leaving her unable to pay her living expenses. She discovered that the funds sent by her friend’s father had been stolen from a UK customer. Because she had promptly withdrawn them, she could not prove that she had not benefited from the fraud.

That was three years ago. Charlie was able to open a bank account in Hong Kong to fund the rest of her studies. However when she tried to set up a UK account with Monzo this summer, she discovered that she was blacklisted. “It turns out my friend’s dad is an accomplished crook and I had no idea that his crimes would have repercussions for me years afterwards,” says Charlie, now 22.

Lloyds agreed to remove her from the national database after Guardian Money provided email correspondence showing that Charlie had been duped. “Where we identify an account has been used to receive fraudulent funds, we take our obligations extremely seriously and take appropriate action with the account holder,” says a spokesperson.

“It’s really important that account holders, and especially students, are aware of the consequences of being caught moving fraudulent funds and more guidance is available via the student account section of our website. Even unsuspecting mules risk being left with no bank account and a damaged credit score.”

Lauren has suffered no financial losses from her brush with money laundering. Nationwide accepted that she had made an honest mistake and is willing to let her open a new account. Emotionally, however, she has paid a high price and still fears the perpetrators might come after her for reporting them. “I still haven’t told any friends or family,” she says. “I wouldn’t want anyone to look at me and think I was the sort of person who would knowingly do this. I’d never heard of money mules until it was too late and it was the mistake of not telling Nationwide what had happened that took over my life.”

* Not their real names