What problems does Least Privilege Security not solve?

Least Privilege Security shouldn't be viewed as a panacea for all security-related problems. It's perfectly possible that malware could install itself by exploiting an unpatched security vulnerability, which might have otherwise required administrative privileges to install. Freely available software on the Internet is often packaged in portable or a per-user form, which usually indicates that it can be installed without administrative privileges. Consequently, Least Privilege Security alone cannot prevent all unauthorized software appearing on your network, and should be used in conjunction with Software Restriction Policy. Least Privilege Security does a good job of protecting critical system components and configuration, but a virus could still infect a fully patched system. The damage would likely be limited to an individual user's profile, leaving the underlying system untouched. This damage limitation mechanism, provided by Least Privilege Security, makes any virus outbreak on your network less serious and easier to clean up.