With vSphere Host Update Utility, you can download and install maintenance and patch releases, which provide security, stability, and feature enhancements for ESXi 4.0 hosts.

You can use vSphere Host Update Utility to check for new release updates and patches that are applicable to the ESXi hosts registered in the vSphere Host Update Utility. vSphere Host Update Utility builds the host list by tracking the hosts that you connect to directly through the vSphere Client. You can also add hosts to the list manually.