1. A computer readable storage medium comprising computer readable instructions configured to perform a method comprising: receiving a first start request to launch a virtual application; instantiating a virtual hard disk comprising a single file, said single file being comprised of a plurality of blocks; establishing a connection to a virtual application server; retrieving a first subset of said blocks from said virtual application server, said first subset being less than said single file; launching said virtual application using said subset of said blocks; performing at least one validation on each of said blocks in said first subset; and storing said blocks in said virtual hard disk.