Microsoft's security chief has unveiled proposals that will see some botnet-infected computers blockedfrom connecting to the internet.

A noted botnet researcher said the proposal didn't attack the problem at its root, and like many technical solutions, was unlikely to do much good.

In a paper, Scott Charney, who heads Microsoft's trustworthy computing group, spelled out a concept of 'collective defence' that he said was modelledn US public health measures including vaccinations and quarantines.

Under Charney's proposal, PCs would be issued a 'health certificate' that showed whether the system was fully patched, that it was running security software and a firewall, and that it was malware-free. Machines with deficiencies would require patching or an antivirus update, while bot-infected PCs might be barred from the internet.

Quarantining PCs could be a last-step measure, Charney said, to keep compromised PCs from threatening others on the web.

"Just as when an individual who is not vaccinated puts others' health at risk, computers that are not protected or have been compromised with a bot put others at risk and pose a greater threat to society," Charney said in a blog. "We need to improve and maintain the health of consumer devices connected to the internet in order to avoid greater societal risk."

Charney admitted that his proposal would face resistance, such as privacy concerns, over what the health certificate would reveal and whether it would be tied to a specific individual. Even so, he made suggestions likely to raise a ruckus.

"There may be value in uniquely identifying devices, as when a device may be infected on a home network," he said in the 'Collective defence: applying public health models to the internet' (download PDF). "It may also be possible, of course, to combine device information with other information to identify a user (much like mobile phones may have unique identifiers and can be tied to particular account holders)."

Charney also said that government intervention would be necessary, another issues the notoriously anti-regulation internet community may balk at. "Voluntary behavior and market forces are the preferred means to drive action but if those means fail, then governments should ensure these concepts are advanced," he said.

The bottom line is that current methods to block criminals from infecting consumers' computers are not working, news that may come as a surprise to Microsoft's own Malware Protection Center, which regularly touts the success of its Windows Malicious Software Removal Tool, a free program that scrubs infected Windows systems.

"Commonly available cyber defences such as firewalls, antivirus and automatic updates for security patches can reduce risk, but they're not enough," Charney said. "Despite our best efforts, many consumer computers are host to malware or are part of a botnet."

Botnets are collections of already hijacked computers that criminals use as a force multiplier to send spam, host malware or launch distributed denial-of-service attacks against websites. A botnet may consist of only hundreds of individual PCs, more likely thousands, and in rare cases, millions.

Carney's ideas are neither new nor untested, as he pointed out in his paper. For example, Comcast, the largest residential internet service provider in the US with an estimated 16.4 million subscribers, recently announced it would notify customers when it detected a bot on their machines. Comcast will direct infected users to a site that walks them through a malware clean-up chore.

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