Europol, Europe's crime agency, has announced that four ringleaders of several cybercrime networks that used botnets, have been arrested in Armenia and Ukraine, with servers across the world including in the UK, the US and Germany taken down, the BBC reports.

The agency said Thursday, May 30 that it has made four arrests but said eight fugitives are on the run. They will be added to Europe’s "most wanted" list.

More than 2,000 websites are now under the control of European law enforcement.

Europol said one of the main suspects had made more than €69 million (£58m) in cryptocurrency through what is known as ransomware - installing software that makes it impossible for a person to access their computer unless they pay a fee.

The malicious software got on peoples' devices mainly through through phishing attempts - such as the kind of emails people are advised not to click on - and compromised websites.

Europol said the take down - dubbed Operation Endgame - is ongoing and it has plans for future busts.