Java is a programming language and computing platform first released by Sun Microsystems in 1995. There are lots of applications and websites that will not work unless you have Java installed, and more are created every day.
IIS is able to impersonate the IUSR_<computername> account because the user name and password for this account are known by IIS. Before returning a page to the client, IIS checks NTFS file and directory permissions to see if the IUSR_<computername> account is allowed access to the file.
Configure the Anonymous Authentication Identity (IIS 7) When you enable Anonymous authentication, you can change the account that IIS uses to access your sites and applications. By default, IIS 7 uses IUSR as the user name for anonymous access. This user name is created when you install IIS 7.