Microsoft on Thursday announced it worked with police in Europe and the United States to disrupt a "dangerous" army of virus-infected computers used to hijack searches at Google, Bing and Yahoo.

Microsoft's digital crimes unit teamed with Europol's European cybercrime centre, the FBI and tech industry allies to tackle a "Sirefef botnet" that commandeers search results and routes queries to websites rigged to infect computers with malicious code, steal information or make money from bogus online ad "clicks."

The botnet, or network of machines infected with a virus that lets hackers take command, is also referred to as ZeroAccess and is believed to have spread across nearly two million computers around the world.

Microsoft estimated the bogus online ad billing and stolen traffic cost advertisers about $2.7 million monthly.

"ZeroAccess targets all major search engines and browsers, including Google, Bing and Yahoo," Microsoft digital crimes unit assistant general counsel Richard Domingues Boscovich said in a blog post.

"ZeroAccess is one of the most robust and durable botnets in operation today, and was built to be resilient to disruption efforts, relying on a peer-to-peer infrastructure that allows cybercriminals to remotely control the botnet from tens of thousands of different computers," he continued.

People's computers typically become infected with ZeroAccess as a result of visiting websites booby-trapped with the malicious software, he said.

Due to the sophistication of the hacker network, Microsoft expected the legal and technical actions taken would significantly disrupt the operation but not wipe it out.

Efforts are being made to get word to people whose computers are infected, and Microsoft is providing virus removal information online at support.microsoft.com/botnets.

Microsoft joins move to encrypt Web traffic
Washington (AFP) Dec 05, 2013 - Microsoft is joining the movement to encrypt traffic that flows across its networks, citing "serious concerns" about government surveillance.

The move by Microsoft follows similar actions by Google and Yahoo in the wake of revelations of vast online surveillance programs led by the US National Security Agency.

"Like many others, we are especially alarmed by recent allegations in the press of a broader and concerted effort by some governments to circumvent online security measures - and in our view, legal processes and protections - in order to surreptitiously collect private customer data," Microsoft general counsel Brad Smith said in a blog post late Wednesday.

"If true, these efforts threaten to seriously undermine confidence in the security and privacy of online communications.

"Indeed, government snooping potentially now constitutes an 'advanced persistent threat,' alongside sophisticated malware and cyber attacks."

Smith said Microsoft said decided to "take immediate and coordinated action" to expand encryption across its services.

It is also stepping up efforts to reinforce legal protections of customer data and is "enhancing the transparency of our software code, making it easier for customers to reassure themselves that our products do not contain back doors."

"For many years, we've used encryption in our products and services to protect our customers from online criminals and hackers," Smith wrote.

"While we have no direct evidence that customer data has been breached by unauthorized government access, we don't want to take any chances and are addressing this issue head on.

"Therefore, we will pursue a comprehensive engineering effort to strengthen the encryption of customer data across our networks and services."

Major tech companies have been seeking to disclose more details about government surveillance in an effort to reassure customers, but have complained that the US government will not allow certain details to be released.