Mark Russinovich, the man behind the indispensable Sysinternals Tools (recently bought by Microsoft) published a
good article about Vista’s User Account Control (UAC) on the TechNet website.
UAC is meant to enable users to run with standard user rights, as opposed to administrative rights. Administrative rights give users the ability to read and modify any part of the operating system, including the code and data of other users—and even Windows® itself. Without administrative rights users cannot accidentally (or deliberately) modify system settings, malware can’t alter system security settings or disable antivirus software, and users can’t compromise the sensitive information of other users on shared computers. Running with standard user rights can therefore reduce urgent help desk calls in corporate environments, mitigate the impact of malware, keep home computers running more smoothly, and protect sensitive data on shared computers.