It depends, but it at least occurs when you are connected to the internet. There are some applications and programs that may auto update. An example is Google chrome browser. Also, if you instal some programs like MS Office professional 2003, MS Info-path is installed by default and any other update in case to 2007 will not remove it. Additionally also when you update some programs, there may be some additional software added by default automatically. However, most program installation, the user is always asked by the comp or laptop by pop up windows to allow or deny the installation.