The ability to create hidden user accounts in Windows can come in really handy. I've setup such accounts on some computers (not mine) for the sole purpose of performing Windows maintenance tasks. Specifically, I schedule JkDefrag to perform weekly disk defragmentations but I find the command prompt that pops up while it runs annoying.
By setting up a hidden account that ugly command prompt can be safely hidden away. Windows automatically logs in with the account to run the scheduled task and logs out silently afterwards. Just remember that scheduled tasks can only be used with password protected accounts.
To create a hidden account, you'll need to first create a new user account the usual way from the User Accounts applet in Control Panel. Be sure to make it an Administrator, or it won't be able to perform system wide maintenance tasks.
Next, run regedit and browse to HKLM\Software\Microsoft\WindowsNT\CurrentVersion\Winlogon\SpecialAccounts\UserList. Edit the value of the key that corresponds to the account name to 0, then reboot and the account will be hidden.
Use Windows Task Scheduler and add tasks to be run using the hidden account at desired intervals, and you're all set.
The Elder Geek - Create A Hidden User Account