Law enforcement officers seized 22 computers and servers in the US and 25 computers and servers in the UK, Netherlands, Latvia, Germany, France, Lithuania and Sweden.
Only two arrests were made, but according to the FBI, analysis of the seized computers is expected to lead to further arrests.
Latvian authorities also executed seizure warrants for at least five bank accounts that were alleged to have been used to funnel profits to leaders of one of the scams.
Typically, victims of scareware are confronted by messages warning their computers are infected with malware and encouraging them to purchase software to fix the problems.
Victims are often sent a barrage of fake virus warnings to trick them into supplying their credit or debit card details to purchase the fake anti-virus software.
One of the crime rings targeted in the international operation used online advertising to spread its scareware products. The tactic, known as "malvertising", hijacks legitimate adverts and modifies them to launch a scareware attack.
"This case shows that strong national and global partners can ensure there is no sanctuary for cyber-crooks," said US Attorney Jenny Durkan of the Western District of Washington.
"We will continue to work with the public and the computer industry, to fortify our cyber defences. A combination of safe online habits and smart technology will help reduce the threat posed by these organised criminal groups," Jenny Durkan said.
US Attorney Todd Jones of the District of Minnesota said: "Addressing cybercrime requires international co-operation; and in this case, the FBI, collaborating with our international law enforcement and prosecution partners, have worked tirelessly to disrupt two significant cybercriminal networks. Their efforts demonstrate that no matter the country, internet criminals will be pursued, caught and prosecuted."
Assistant director Gordon Snow of the FBI's Cyber Division said: "Scareware is just another tactic that cyber criminals are using to take money from citizens and businesses around the world. This operation targeted a sophisticated business enterprise that had the capacity to steal millions."
Cyber threats are a global problem and no single country working alone can be effective against these crimes, Gordon Snow said. He thanked all the foreign law enforcement agencies for their ongoing partnership and commitment in disrupting the threat.
This story was first published by Computer Weekly