User Account Control (UAC) was probably the first new feature of Windows Vista that most users encountered, and received considerable attention when the OS was released. UAC gives a way for users to act as computer administrators just for administrator tasks. This is important to only allow software that requires elevated rights to run with such powerful (and potentially dangerous) rights. Over time, UAC prompts have diminished, especially with the release of Windows 7. But it's clear malware authors really hate UAC.