Virtualizing is the act of operating from a virtual machine. This enables you to acquire any number of rootkits, worms, trojans, spyware, and other unwanted software without the fear of persistence, since a new virtual machine can be started at any time.
The problem with virtual intrusion prevention is that it is limited to file operations. Unfortunately, malware can target e-mail and shared file resources that are persistent. In addition, removing malware by restarting your virtual machine doesn’t help the 20 friends you inadvertently infected before you realized something was amiss.