Twenty-one arrests have been made across the UK as part of an operation into an online marketplace that advertised stolen personal details, the National Crime Agency (NCA) said.

Those targeted were UK-based customers of WeLeakInfo, a criminal website that hosted 12 billion stolen credentials from more than 10,000 data breaches, according to the NCA.

The website was taken down in January 2020 following an investigation by the agency.

It said cyber criminals paid for access to the website in order to download personal data for use in further criminality, including cyber attacks and fraud offences.

The operation, which ran over the past five weeks, was co-ordinated by the NCA and involved cybercrime teams from across the Team Cyber UK network.

The NCA said that of the 21 arrested – all men aged between 18 and 38 – nine were detained on suspicion of Computer Misuse Act offences and nine for fraud offences, while three are under investigation for both.

Officers from the agency conducted 11 of the arrests and seized over £41,000 in bitcoins.

Some of those arrested are also believed to have purchased other cybercrime tools, such as remote access Trojans (RATs) and crypters.

Three of those held were also found to be in possession of, or involved with, indecent images of children, the agency said.

Another 69 individuals in England, Wales and Northern Ireland, aged between 16 and 40, were visited by Cyber Prevent officers warning them of their potentially criminal activity, with 60 served with cease and desist notices.

Paul Creffield, from the national cyber crime unit, said: “Cyber skills are in huge demand and there are great prospects in the tech industry for those who choose to use their skills legally.

“Cyber criminals rely on the fact that people duplicate passwords on multiple sites and data breaches create the opportunity for fraudsters to exploit that.

“Password hygiene is therefore extremely important.”

Advice and guidance on how to mitigate against cyber attacks can be found on the National Cyber Security Centre’s website.