Ordinarily, when you install a service, it runs under the LocalSystem account. You can see this by opening the services management console, right-clicking on a service, selecting Properties, and choosing Log On tab. LocalSystem is a special account used by the SCM that gives wide-ranging privileges to interact with the computer. If you'd like to give your service more limited access, you can assign it to another user account.
Two accounts that you might consider are
LocalService and NetworkService. These accounts have fewer privileges than LocalSystem, but are still built-in and ready to use. To set a new user account for your service, add the Account and Password attributes to ServiceInstall. If the account doesn't have a password, which is the case with LocalService and NetworkService, you can omit the Password attribute. Here's an example:
<DirectoryRef Id="INSTALLFOLDER">
<Component
Id="CMP_WindowsService1"
Guid="3D3DE5C1-7154...