When we talk about Money Laundering, these "geniuses" have found in these failures a way to introduce into the legal financial system, enormous amounts of money from illicit sources (generally the product of drug trafficking and corruption) which should be monitored by the authorities. In fact, most of the time the authorities would be looking for tax evasion (You know, the coveted taxes).

Why do criminals need to make their money legal?

Accumulation.
Generally, the money from drug trafficking is handled in cash. We are talking about the most lucrative economic activity in the world.
By talking about 6 or 7 figures regular cash income, we would be referring to a situation where you couldn't get rid of that money fast enough.

Keeping it in a safe in your house, would imply a potential theft. If you need to take a trip or go live in another country, you could not take it with you.
You couldn't buy a new car or a big mansion without drawing the attention of the authorities.

Placing it in the bank through multiple small deposits is also not an option, you would be committing a federal crime called "Structuring." In fact, people have been convicted of structuring ... simply for making large cash deposits. With absolutely no connection to drugs or other illegal conduct.

In short, there are many systems dedicated to tracking illicit enrichment, so very little is worth 100 million dollars cash in a safe if you can not spend them.

What does a "Bleaching" genius do?

Perhaps you will start by acquiring a legitimate business, one that handles cash transactions. Just for example, let's say a pawn shop. At the end of the day you take your cash deposit to the bank and deposit it in the commercial account of the business. Your accountant records the income. You pay your taxes for it. Bingo!

But when the flow of money from illegal activity far exceeds the limit that your legal business can generate daily, you fall back into the problem of accumulation.

It would take thousands of pawnshops, thousands of testaferros to hide so much money. Maybe you could spend years doing this activity successfully, but the time will come when you won't be able to hide it anymore.

The creation of Ghost Businesses is another method of money laundering.
Public limited companies can be created in tax havens such as Switzerland and the Cayman Islands.
Once the company is created, it can create false transactions such as payment for goods and services that are paid for with its dirty money.

They can also turn to the stock market, applying a technique called "mirror trading."
In this method you use your dirty money to buy shares, then you self-sell your shares for the same amount somewhere abroad. The transactions functionally cancel each other, but at the end of the round, you have converted your dirty dollars into clean Rubles.

The new era: Crypto-Laundering

In 2015 the movie "Dope" was released, where it was shown how Bitcoin was used for the sale and purchase of drugs without a trace.

The main method of laundering money from cryptocurrencies is using "mixers" services, which take virtual currencies from different clients and deposit them in a "pool", moving them from one point to another to confuse their origin.

These services are called mixers, turners, nebulizers, and laundries. They capture funds from multiple clients, mix those funds, and then issue the mixed funds. They generally charge between 1% and 3% per transaction for their services.

The key to this “mixer” is that it does not request information from any account or any personal information at the time of making the transaction and, in addition, it does not keep any record of the activities carried out by its visitors.

Anonymity is the main attraction that this service offers.