You have to plan for the unexpected, no single piece of software is going to give 100% protection. For the most part prevention is much better than cure, there will always be zero day malware that perhaps even heuristics won't detect so you have to take measures to limit the potential damage and stop it from getting established.
Malware needs permission to place files in the system folders and to create registry entries and they get this by inheriting your logon account privileges, so if you have admin privileges so will the malware (unless you do something about it) and it will be able to get into system folders and create registry entries, etc.
You might also consider proactive protection, in order to place files in the system folders and create registry entries you need permission. Prevention is much better and theoretically easier than cure.
Whilst browsing or collecting email, etc. if you get infected then the malware by default inherits the same permissions that you have for your user account. So if the user account has administrator rights, the malware has administrator rights and can reap havoc. With limited rights the malware can't put files in the system folders, create registry entries, etc. This greatly reduces the potential harm that can be done by an undetected or first day virus, etc.
Browsing the Web and Reading E-mail Safely as an Administrator. This obviously applies to those NT based OSes that have administrator settings, winNT, win2k, winXP. Check Bob's, setup instructions and importantly the dropmyrights.msi file needed as MS have now cleared the original link.
http://mysharedfiles.no-ip.org/dropmyrightsIf you have Vista the UAC attempts to do this for you by requiring a password for tasks that would require admin privileges.
Unfortunately this isn't available in XP (until recently forum Search for SuDown) or win2k so DMR is an option to help limit any potential damage.
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