One of the world's largest cybercrime rings have been operating under the radar for quite some time now, stealing over $500 million from user's bank accounts from over 80 countries worldwide.

The FBI along with Microsoft's Digital Crimes Unit shut down servers that were being used by as many as 5 million infected PCs. The sophisticated online crime operation was operated by the Citadel network. They managed to run the botnets for 18 months, successfully stealing money from unsuspecting victims.

Local police forces and tech companies in the 80 countries that money was stolen from participated in the shut down. About 1,000 of the 1,400 or so networks that made up the Citadel botnet are believed to have been wiped off.  A botnet is comprised of hundreds to thousands of infected PCs that respond to commands routed through a command-and-control server, which is also an infected PC.

The Citadel cyber crime unit are reported to have used over 5 million PC's infected by the malware.

"The bad guys will feel the punch in the gut," said Richard Boscovich, a spokesman for Microsoft's digital crimes unit, BBC news notes.

In a blog post, Microsoft said this was its "most aggressive botnet operation to date" and the "first time that law enforcement and the private sector have worked together" to "execute a civil seizure warrant as part of a botnet disruption operation."

Computers used in this cyber crime operation were able to break into thousands of users bank accounts, ranging from American Express, Bank of America, Citigroup, Credit Suisse, eBay's PayPal, HSBC, JPMorgan Chase, Royal Bank of Canada and Wells Fargo.

A civil lawsuit has been filed by Microsoft in the U.S. District Court in Charlotte, North Carolina against the mastermind and leader behind the operation which has only been identified as John Doe No. 1, aka Aquabox.

"In addition, the FBI is working with Europol and police forces in many other countries to track down and identify the 81 'lieutenants' that helped Aquabox keep Citadel running," the BBC reports.