The IIS Application Pool Process and Windows Account Privileges

w3wp.exe is the IIS application pool process. Application pool was a new feature in IIS 6.0allowing isolation between different web applications. Each application pool runs in its own worker process, so exception in one won't bring down another. App pools can be configured to enhance reliability but also for security e.g. lower security apps could belong to a common pool. Running the worker process using a LOW PRIVILEGE account, you minimise security implications.

In pre-version 6.0 IIS, worker processes used to run as LocalSystem. This had security implications. Now the default account is NetworkService, which has low-level access rights.