1. A computer-implemented method for use with a launching application and a separate runtime engine, the launching application and the runtime engine being configured to access a shared memory location, the method comprising: at the launching application, receiving a first instruction to execute a virtualized application file and a ticket, the ticket comprising a digital signature and an expiration date; at the launching application, storing the ticket in the shared memory location and sending a second instruction to the runtime engine instructing the runtime engine to execute the virtualized application file; and in response to the second instruction received from the launching application, at the runtime engine, reading the ticket from the shared memory location, determining whether the digital signature is valid, determining whether the ticket has expired, and executing the virtualized application file only when the runtime engine determines the ticket is valid and has not yet expired, whether the ticket is valid being determined based on the digital signature, and whether the ticket has expired being determined based on the expiration date.