It's a bit blunt summary. I will write a loose explanation based on a Dutch history TV programme's blog post, this event is called the "Lieftinck Tenner". [1]

A few weeks after the new post-war government was installed, all hundred currency notes were declared invalid, out of the blue. All hundreds could be taken to the bank, where they were put on a blocked account for an indefinite period. Anyone who could not prove that they obtained the money in a honest way, their money would be taken and they would also be put on trial for black market trading. It was a rare case of the burden of proof being reversed in NL.

The confiscation of the hundreds was only just the beginning. The next step was that all Dutch paper money was invalidated in one swoop on 26 September 1945. At the same time, all bank accounts were frozen. Everyone was given a week to bring their money to the bank. Everything was registered, including foreign currency holdings, life insurance contracts and recently concluded mortgages. Only the coins remained outside this purification. Salaries were not paid that week as not to disrupt the system; the following week the pay packets were doubled.

For a week, from 26 September to 2 October, everyone had to survive on exactly the same amount: the famous "Lieftinck Tenner". For a short while, there is total economic equality in the Netherlands. It was not a tenner by the way, it was five notes of one guilder (1) and two of one rijksdaalder (2,50). It was a conscious decision not to pay out the money in one banknote, but in different denominations because no one else would have change.

Lieftinck, the economic minister at the time, explained: “Money purification is not only necessary to track down black market profits and to hit those who have made black market profits, but also because, after five years of German extortion, we are as destitute as no one could imagine. Limiting the circulation of money must prevent disloyal elements from stealing all the available goods from the market due to their excess of money, whereby people with small fixed incomes will be duped.”

From 3 October 1945, the money that has been frozen was gradually unblocked and replaced by freshly printed banknotes. There are only a few hundred million guilders of new money available, barely enough to pay wages. Lieftinck wants to hold on to the surrendered money for as long as possible, to prevent inflation and to detect the illegal war profits. As long as the monetary balance has not been restored, everyone gets enough money to live on, but it is not much. In retrospect, it is unbelievable how the whole of the Netherlands obediently accepts that Lieftinck keeps the piggy bank locked up indefinitely. The realisation "that it is simply necessary" was so widespread in the country that there was no notable protest against the blockade.

(Also, in order to complete the monetary purification, Lieftinck introduced two drastic wealth taxes: a one-off wealth tax, and a special levy on capital obtained during the war. The latter levy in particular could be quite high: anyone who could not prove how they earned their money during the war was assessed 90% and thus lost almost everything.)

The monetary purification was not completed until 1952, when the last amounts were unblocked. In seven years, Lieftinck had thoroughly reorganised the economy. The monetary balance has been restored and, moreover, the banking system has been unintentionally stimulated enormously. Thanks to the purification measures, for the first time in Dutch history almost everyone has a bank account, which means a huge boost for the Dutch banks.

It is not sure if this move was also succesful in actually punishing the people that made cash profits during the war - there was a huge flight in capital goods of gold, jewelry, land, houses. Another example is a farmer laundering his money by buying a bull for hundred times the real price. Some researchers claim the government might have emphasized dealing with the war profiteers because such a radical national economic effort would not have received as much support otherwise.

[1] https://anderetijden.nl/programma/1/Andere-Tijden/aflevering...