Microsoft's Corporate Vice President for Trustworthy Computing, Scott Charney, is advocating banning infected PCs from the net. There is also a write-up at the BBC about this. I'm for the idea mostly. Sure, the Internet is supposed to be about absolute freedom and anonymity, but at the same time, it costs money to keep the net running, and if a system is causing trouble, there should be a way of dealing with it. I remember reading somewhere previously about how an ISP could clearly see systems that it was giving access to the net were infected, because they were broadcasting spam or contacting known URL's associated with malware, but they couldn't do anything to stop it because legally they aren't allowed, and even contacting the people who's computers were infected would likely get it in trouble for some type of privacy infringements. Personally, I expect my ISP to watch my traffic at some basic level. Whether it's to improve performance, or what, I wouldn't be surprised or angry if I found out my ISP could tell if a machine I was on was infected, and if it contacted me about it, I'd be grateful. I think ISPs should contact users when their machines are infected, and if after a few days the problem is still occurring, then the ISP should restrict you to a single site that you have to click through to get Internet access, much like when you try to get Internet access at starbucks or hotels, but instead of putting in your credit card number to get Internet access, you have to acknowledge that you are aware your PC is infected, and you should then be required to either explain to your ISP why it's not a problem (possibly via some out-of-band mechanism so the malware can't manipulate this), or you'll then be given 24 hours to fix it, or else you're PC will be permanently blocked from the net excepting a single page with a A/V download on it, until you're PC no longer appears infected.
I think the idea of "health certificates" advocated in the BBC article won't work, and sure this could snowball into greater privacy infringements and restrictions on freedom, but I think it's time is coming.