Security researchers have uncovered a fast-growing worldwide botnet of 1.9 million government, corporate and private computers, it was revealed today.
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The botnet has been in use since February and is hosted in the Ukraine, according to a report by security firm Finjan.
They have tied the botnet to a six-member cybergang that was selling control of batches of 1,000 compromised computers for as little as £30 to £70.
The cybercriminals were enable to infect end-user computers through legitimate websites with malware that bypassed 90% of common anti-virus software.
The malware is designed to work in the Windows XP operating system and takes advantage of security vulnerabilities in a range of browsers.
Most infections (78%) were through Microsoft's Internet Explorer browser, followed by Mozilla's Firefox (15%), Opera (3%) and Safari (3%), the report said.
The malware enabled the cybercriminals to execute almost any command on targeted machines, including copying files and recording keystrokes.
The botnet was uncovered when the researchers traced calls from a Trojan back to its command-and-control centre.
UK government computers were among the compromised computers in 77 government-owned domains, the researchers found.
Finjan alerted US and UK authorities and notified government departments and businesses whose computers were part of the botnet.
UK police are liaising with other international agencies involved in the investigation.
"No other information can be revealed," said detective chief inspector Charlie McMurdie, who heads the investigative arm of the Police Central E-Crime Unit (PCeU).
The sophistication of the malware and rapid infection rate proves cybercriminals are raising the bar and shows how vulnerable organisations are to this type of attack, said Yuval Ben-Itzhak, CTO of Finjan.
The fact that the malware bypassed such a high percentage of anti-virus products shows the need for a multi-layered approach to defence, he said.
According to Ben-Inzhak, signature-based detection methods are no longer effective against rapidly changing malware.
Instead, organisations need to combine web security, data leakage prevention and URL filtering to strengthen the network perimeter.
It is easier to control what comes in and out of the corporate network than to patch every browser ad-on, which is usually slow and difficult to manage, he said.