Most Windows software these days follows the convention introduced back in Windows 95 to install applications into the “Program Files” or “Program Files (x86)” folder on your computer (usually located in C:\). With more recent versions of Windows such as Windows Vista and Windows 7 this has become quite important as the “Program Files” folders have special permissions set on them to prevent potentially malicious software from undertaking unwanted activity on your computer such as modifying itself or other files.
In this situation, UAC (User Account Control) would alert you if an application required elevated rights. You could safely decline the opportunity if you weren’t expecting elevated rights to be required when launching an application and back out of a potential attack. However, if you had installed an application to another folder or even another drive you won’t have UAC protecting the files in that folder which would be a potential attack vector for malicious software.
So next time you install new software just make sure it is going into the “Program Files” or “Program Files (x86)” folder (the x86 folder is for 32-bit software on 64-bit Windows installations). It could save you from problems later on.