Thousands of websites around the world, including many operated by governments, were infected by hackers to silently "cry out" cryptocurrencies, security researchers said.

It is the first time that an attack of these characteristics is made public, in which a new class of hackers seized a large number of websites to create currencies such as Bitcoin, which are generated through the use of computing power.

The attacks, which were unveiled at the weekend by British security investigator Scott Helme, affected more than 4,000 websites, including those of the British data protection and privacy agency and the United States federal court system. United.

Unlike traditional attacks, these infections do not contain "ransomware" or steal data, but operate in stealth mode to obtain benefits from the dark world of cryptocurrencies.

Helme said in a blog post on Sunday that hackers were able to access a large number of websites by infecting a commonly used "plug-in," or some software that helps sites work better.

In this case, the hackers used the malicious software to create Monero, one of the new cryptocurrencies that are causing a sensation in the financial markets.

"If you want to load a cryptocurrency collector on 1,000 websites, you do not attack 1,000 websites, you attack website 1 from which they all load the content," he said.

The creator of the plug-in, the British software firm TextHelp, said it removed the affected software online after it discovered the "attempt to generate cryptocurrencies illegally".

"This was a crime and a thorough investigation is currently under way," the company said in a statement.

Researchers have been warning in recent weeks about this type of malware, which can act and generate benefits for third parties without the users of the team noticing.

Cisco security researchers Talos warned last month that this type of hacking "has increased exponentially."

Because of the huge financial gains from cryptocurrencies, Cisco researchers said they have become a major target for hackers.

"In general terms, mining simply uses the resources of the system to solve large mathematical calculations that result in a certain amount of cryptocurrencies being granted to the solvers," the Cisco researchers wrote in a research note.

Security researcher Graham Cluley said that this attack highlights the vulnerabilities of websites that may have weaknesses in third-party components.

"Things could have been much worse," Cluley said in a blog post. "Imagine if the plug-in had been tampered with to steal login passwords instead of stealing CPU resources from the computers they visit."