Actual reports are here, downloadable as PDF:

http://www.nsslabs.com/reports/your-browser-putting-you-risk...

http://www.nsslabs.com/reports/your-browser-putting-you-risk...

The methodology is (vaguely) described in the first document. The click fraud result was very interesting, it seems that Chrome just doesn't address it at all. Of course I suspect the majority of click fraud goes on in Google's ad network, so Google has an incentive to ignore it just as Microsoft has a reason to catch it.