Image copyright Getty Images Image caption Organised criminals want people to help them move their money without detection

Earning extra money for doing very little - sounds great, doesn't it?

The catch? Let a large sum of money pass through your bank account and don't ask any questions about where it came from or where it's going to.

Now you're probably having second thoughts about signing up.

This is the world of so-called money mules, which one Belfast judge has described as a developing "cottage industry" enabling organised gangs to launder the proceeds of their crimes.

In separate cases this week, two women aged in their 30s from Belfast were in the dock at the city's crown court for their roles in organised bank fraud after making their "clean" accounts available to criminals to deposit sums of up to £10,000.

The money in one of the cases had been traced back to a bank fraud in January last year in which the victim had £47,000 stolen from their account.

Neither woman had a criminal background - the judge described one as "intelligent... [and] capable of having a 17-year work history and two kids", while the other is a carer for her disabled son.

Now they both have a serious criminal conviction that could have a long-lasting negative effect on their lives.

What is a "money mule"?

A "money mule" is someone who agrees to share their bank details and criminals' cash is then deposited in their account.

They are then asked to send the money to another bank account and are paid for doing so.

Image copyright Getty Images Image caption The transactions are often quick, with stolen money going into an account and straight out of it

It is a method used by criminals to make their profits more difficult for police to trace.

There are typically two types of people involved in "money muling".

There are those who knowingly launder money to further their own or other people's criminal enterprises.

And there are those who are enticed to do it as a quick earner, maybe for £100 or £200.

Those in that second category tend to have "no real criminal intent", according Ch Supt Simon Walls of the Police Service of Northern Ireland (PSNI).

"What they don't realise is they're committing a serious criminal offence - they're laundering money," he told BBC News NI.

As Judge Neil Rafferty told one of the women in Belfast this week: "A little word of advice: there is no such thing in life as a free lunch."

How do people become involved in it?

Criminal recruiters - referred to as "herders" - can make personal approaches or use social media and make "money muling" as attractive as they can, according to police.

They offer a generous, quick return for what seems to be a simple process.

Image copyright PA Media Image caption Social media platforms are used by "herders" to recruit "mules"

UK Finance is a body that represents banks and it tries to raise awareness of what "money muling" is and how to avoid it through its Don't Be Fooled initiative.

It told BBC News NI that adverts on Facebook, Instagram and Snapchat are commonly used to draw people in.

"They feature pictures of people with high-value goods, big wodges of cash and slogans like 'earn money quick' and 'instant cash in your bank'," said Sarah Sinden of UK Finance.

Once someone is initially recruited, she said, the conversation moves to a messaging platform such as WhatsApp where the content can be concealed.

Who is being targeted in that way?

As this week's examples in Belfast show, people with no involvement in crime are wanted by the "herders".

That is because their clean, well-established bank accounts make it easier for criminals to hide their dirty money from police and banks.

Speaking in court this week, Judge Rafferty said those people were prepared to "sacrifice their good name and their liberty" to become involved.

Ms Sinden said students, young people and other low-income earners are the most vulnerable.

"That generally tends to be because they're looking for ways in which they can earn money quickly," she added.

Image copyright Pacemaker Image caption People who take part in "money muling" often do not know they are committing a crime, says Ch Supt Simon Walls

Ch Supt Walls said: "Coming up to Christmas, for people needing a few quid or who have high expectations of what they want to buy for family and friends, this might seem like an attractive option - but it ain't."

The PSNI has gone to schools and colleges to raise awareness of "money muling", warning students that if they are caught it could affect the rest of their lives.

It is also part of the Scamwise NI Partnership, which offers advice on how to spot scams and report them.

What are the consequences?

Police say "money mules" support serious crime including drug dealing, human trafficking, counterfeiting goods and even terrorism.

UK Finance points out that those who are caught will pay a heavy price in their personal finances.

Ms Sinden added: "They will have their bank account closed, will find it hard to get access to credit and they'll struggle to even get a mobile phone contract."

But a conviction could have even more serious consequences.

At Belfast Crown Court, Judge Rafferty said those who had so far admitted the crime had been freed on suspended jail terms.

But he warned that anyone else caught would go to prison because that would be the "only way to stop it".

Ch Supt Walls said: "People see these adverts online and just don't know what they're getting themselves into.

"They could be standing in the dock of one of our courts, facing a judge handing down a custodial sentence.

"For most people a custodial sentence is devastating - some people lose their jobs, some people lose their families."