This is achieved through the use of a filter driver and layering technology Altiris acquired from FSLogix.
Altiris was acquired by Symantec Corporation in 2007, who are the makers of Norton AntiVirus, amongst other things.
In 2008, Symantec acquired AppStream to incorporate the streaming of virtual applications.
[1] According to a quote from DABCC.com, this will "deliver virtualized, on-demand application delivery and management".
[2] Previous names for SWV are the before-mentioned SVS and Software Virtualization Professional.