A computer virus trapping device (10) is described that detects and eliminates computer viruses before they can enter a computer system and wreck havoc on its files, peripherals, etc. The trapping device (10) creates a virtual world that simulates the host computer system (28) intended by the virus to infect. The environment is made as friendly as possible to fool a computer virus into thinking it is present on the host (28), its intended target system. Within this virtual world, the virus is encouraged to perform its intended activity. The invention is able to detect any disruptive behaviour occurring within this simulated host computer system. It is further able to remove (52) the virus from the data stream before it is delivered to the host (28) and/or take any action previously instructed by a user (38).