Many believe that it was designed to attack important industrial facilities in Iran including the Bushehr nuclear power plant which was originally due to open last month.

After it has hijacked a PC, Stuxnet looks for Siemens software that runs industrial control systems in facilities like factories and power plants.

It then launches an attack by reprogramming software to give any industrial machinery new, potentially dangerous, instructions.

It is capable of taking control of key processes and is able to set off a sequence that could cause the entire system to self-destruct, say experts.

David Emm, a senior security researcher at Kaspersky, said what made Stuxnet different from other viruses was its targeted nature.