Game over Zeus.
The action related to a strain of malware - meaning malicious software.
Malware is typically downloaded by unsuspecting users via what is known as a phishing attack, usually in the form of an email that looks like it comes from somewhere legitimate - such as a bank - when it fact it is designed to trick a person into downloading malicious software.
Once installed on a victim's machine, Game over Zeus will search specifically for files containing financial information.
If it cannot find anything it deems of worth, some strains of Game over Zeus will then install Crypto-locker - a ransom-ware program that locks a person's machine until a fee is paid.
The FBI said Game over Zeus could be responsible for "financial losses in the hundreds of millions of dollars".
In what has been described as the biggest ever operation of its kind, servers all over the world were raided simultaneously by the authorities.
"The scale of this operation is unprecedented," said Steve Rawlinson from Taga-dab, a web hosting company involved in the take-down effort.
"This is the first time we've seen a co-ordinated, international approach of this magnitude, demonstrating how seriously the FBI takes this current threat."
Rory Cellan-Jones reports on a "powerful computer attack", which people have two weeks to protect themselves from
The action meant the authorities could direct what are known as Command and Control (C&C) servers - the machines that control the operation of the bot-net.
With the C&C servers under police control, criminals should temporarily be unable to manage the computers they hijacked - but only until they are able to set-up new C&C servers elsewhere.
All computer users are being urged to make sure that the malware has not infected their machines.
"This warning is not intended to cause you panic but we cannot over-stress the importance of taking these steps immediately," said UK-based Get Safe Online, a government-backed organisation that has published a list of software it recommends for the task.
"This is because the UK's NCA has taken temporary control of the communications used to connect with infected computers, but expects only a very limited window of opportunity to ensure you are protected."
Technical problems caused some users to become unable to access the Get Safe Online website on Monday afternoon.
A spokesman said: "We have been overwhelmed by the interest of those trying to take action to protect themselves by visiting our page.
"We are sorry about this and are working very hard to make the page available as quickly as possible. In the meantime, the advice can be accessed via our Facebook and Google+ pages."
More detailed information on the threat was published by the US Computer Emergency Readiness Team (Cert).
Following a slew of high-profile hack attacks in recent weeks - including eBay, Spotify and shoe retailer Office - security expert Rik Ferguson raised concerns that computer users might be suffering from "notification fatigue".
However, he stressed that this operation was more targeted, and should not be ignored.
"I think one of the things that is really critical with this operation is that if people are infected, it's going to be completely invisible to them," the Trend Micro security researcher said.
The FBI said cooperation with Russian authorities had been "productive"
"One of the strengths of this operation is not only that it involved organisations around the world, but that it involved the ISPs as well.
"The ISPs will go out and pro-actively notify any of their customers who are infected."
He suggested that machines known to be infected by serious malware should be placed in a quarantined environment until the threat was removed.
"Making it uncomfortable, if not impossible, to use the internet is one of the most effective ways to do that," he said.
Hi-tech crime terms
- Bot - one of the individual computers in a bot-net; bots are also called drones or zombies
- Bot-net - a network of hijacked home computers, typically controlled by a criminal gang
- Malware - an abbreviation for malicious software ie a virus, Trojan or worm that infects a PC
- Ransom ware - like malware, but once in control it demands a fee to unlock a PC
This also relates to your mobile phone, if you use it for on line or to access your PC at home or Office / Business.
- Make sure all of your files including documents, photos, music and bookmarks are backed up and readily available in case you are no longer able to access them on your computer
- Never store passwords on your computer in case they are accessed by Game-over Zeus or another aggressive malware program
- Be weary of clicking on LINKS in an Email, as this may send you to a hacker/ spoof site.
- When installed! This also collects your social media info, scanning for subject matter to help Infiltrate, this could be some security info you have stored on your social site.