In a computer system, a virtual machine (VM) guest is instantiated on a VM host. The VM host detects a plurality of successive universal serial bus (USB) events occurring in the computer system and compares the plurality of successive USB events to a preset criterion. When the plurality of successive USB events meets the preset criterion, the VM host transmits a request for triggering an operation mode to the VM guest. The VM guest executes a control program for initiating the operation mode in response to the request.