Methods, computer program products, and systems are presented. The methods include, for instance: synchronizing, by one or more processor, first virtual machine(s) with a second virtual machine, the synchronizing comprising mirroring first input events to the first virtual machine(s); and customizing, by the one or more processor, the first virtual machine(s), the customizing comprising suspending the synchronizing and facilitating sending of second input events to the first virtual machine(s). In one embodiment, the synchronizing comprises cloning the second virtual machine to create the first virtual machine(s), the cloning comprising initializing the first virtual machine(s), and copying second virtual machine state information to the first virtual machine(s). In another embodiment, the customizing comprises decrementing an available first virtual machine counter, and the synchronizing comprises cloning the second virtual machine to create another first virtual machine responsive to the available first virtual machine counter having a certain value.