One of the problems with Windows security is that practically everybody runs in root (admin) instead of user mode. One of the problems is that, historically, a lot of software has been written to run in that mode. However, it seems MS is finally about to bite the bullet with Longhorn, according to an interview with Jim Allchin in Information Week:
[On other security matters] Longhorn will run as standard users, instead of admin [users]. Today in most installs, a large majority run as admin, so everything on the machine has full rights. Longhorn will run as a standard user, with limited user rights that can't impact the operating system or the user.
For example, if you would try to access something, you'd be prompted to elevate your privileges. Beyond that we have work going on to isolate even the new standard-use level so Internet browsing can run in a more isolated environment and, as necessary, switch from intranet to Internet in a seamless way. The probability of contamination from working on the Internet and having it contaminate the intranet is dramatically dropped.
