Hi,

The hotfixes can contain any number of updates to the operating system. Typically, they'll release new or updated device drivers (software that allows for plug and play with differnt printers, etc), fixes to various bugs in the OS, fixes for possible security issues, etc.

Usually an updated hotfix comes with Release Notes, which lists exactly what the fix is doing.

As a rule of thumb, never download anything from Microsoft the day it becomes available. Even their fixes are notoriously buggy. They'll fix them once enough people complain. I wait a couple of weeks and then download once someone else has reported the inevitable problems.