Prior to SCCM 2012 SP1 there was no way to hide a Task Sequence from the Software Center, therefore all Task Sequences are available for the end user to install.
There is a work around that will remove the TS from the Software Center but keep it available as a option during the OSD process.
To do this right click any TS that you want to hide and choose Properties.
Click the Advanced tab and select ‘Run only on the specified client platforms’. Select an O/S that you are not deploying the image to.
This has been addressed in SCCM 2012 SP1. See here.
SCCMentor - Paul Winstanley 
Or just don’t advertise it to “All Devices”, but to an Admin user 😉 (ie. let the admin log in to get access to the TS)
\Software Library\Overview\Operating Systems\Task Sequences\MyTS
in bottom TAB “Deployments”
“Operating System Deployments” -> Properties
on tab “Deployment Settings” choise “Only media and PXE”
enjoy!
That is true but then it’s available to anyone booting up via media or PXE and you may not want this scenario.