Among the new monetary systems that have emerged, in relation to the possibility of installing computer programs on their blockchains, the development of Ethereum stands out, created by the Russian programmer Vitalik Buterin. These programs, which are deployed on the chain, are called smart contracts, in honor of the cryptologist Nick Szabo who published an article in 1995 in which he described a form of a computer program that runs by itself. The smart contracts deployed on public blockchains are not able to run themselves but have decided to keep the name. And, although the translation of smart contract into Spanish would be that of smart contract, this program is neither a contract nor is it intelligent; it's just a code. A smart contract is a computer code deployed on a chain of blocks that a third party can activate to execute an action. Said action will only be the one for which the smart contract has been programmed. And the third, which in certain cases can be called 'oracle', will drive, normally by paying for it a number of electronic coins to the miner who keeps the program, the execution of the action when he himself has verified that a condition has been met. Therefore, let us completely discard, because it is not at all close to reality, the hackneyed definition of the smart contract as a smart contract that executes itself when it verifies a condition. Some examples of smart contracts are those programmed to function as crowdfunding or fundraising systems for projects or user identification systems, to allow third parties to access personal data hosted on platforms outside the network, as well as to withdraw this permission. access. ICOs are a quite revolutionary type of smart contract that is causing limitations and even state bans for their use or promotion. An ICO or Initial Coin Offering development is a financial instrument through which an interested party generates, through a smart contract, a series of digital assets called tokens, whose acquirers can transfer to third parties through a secondary market. ICOs are regulated in practically every region and state in the world, including Europe and the United States. However, some users are using them as illegal systems of financing, movement of capital or the incorporation of companies that must be registered or whose partners or participants must be or be able to be known. In the same way that the regulations of regulated markets and the incorporation of companies with one technology must be complied with, another must also be complied with. One of the most interesting cases, which has led the United States Market Supervisor to publish in 2017 the notice “ SEC Issues Investigative Report Concluding DAO Tokens, a Digital Asset, Were Securities” Was the smart contract known as The DAO, deployed on the Ethereum network by a group of people, led by Christoph Jentzsch. In a few days, 11,000 users linked to the program a number of ethers equivalent to 160 million dollars. However, a user took advantage of an error in the program code to initiate the extraction of tokens worth 50 million dollars. To try to prevent that user from using the coins they mined, the creators of Ethereum developed a new version of the ethers mining software that made those mined tokens invalid. Some of the Ethereum miners did not install this update and as a consequence, two lines of different ethers were created: Classic Ether, among which are the stolen; and New Ethers. It is not known who the affected users are and the identity of the one who extracted coins is unknown. What is known is that the United States Government has recalled in writing that, despite new technologies, the laws to create companies or financing systems must continue to be complied with in the same way. The possibility of anonymity that an ICO offers, its link to the theories of crypto-anarchism, and the clear advantages it offers for tax evasion have sadly caused its illegal use, even linked to criminal purposes, to be worrying. Countries such as China, through an official statement from seven entities, including the People's Bank of China, have declared all kinds of ICOs illegal, as well as their promotion and support, both by individuals and by financial entities, forcing restitution of the money paid for the tokens and the paralysis of all activity related to them within its borders. Counting both successful and unsuccessful ones, as well as 10%, according to the People's Bank of China, which are fraudulent or scams, ICOs reach an average capital raising equivalent to one and a half million euros each, for a total of more than 1,300 million euros raised for projects. The ICO market is attractive to investors and companies around the world. That some private parties break the law does not mean that doing ICOs is illegal, so there are already companies in Spain launching ICOs. Electronic currencies, blockchain, and smart contracts are current technological solutions that offer endless possibilities. However, the fact that the technology itself is legal does not mean that all uses made of it are also legal. Therefore, an era of research and innovation opens for companies and governments to promote the use of these new technologies to improve services and create new economic models along the path of legality.