Watch out - the invisible virus is on its way

The metamorphic virus - a cousin of the simpler polymorphic virus - will alter itself each time it is forwarded, rendering it invisible to conventional virus scanning software. Although the virus is currently only conceptual, security experts claim it will become a common threat once the source code becomes readily available to virus writers.

The viruses will become increasingly sophisticated, according to Eric Chien, chief researcher from Symantec. "Over the next three years we will see a proliferation of metamorphic viruses as the current viruses in the wild aren't very smart. Viruses such as the Kournikova or Love Letter can be recognised by their so-called 'fingerprints' or code patterns, but the metamorphic virus will alter its code each time it is forwarded," he said.

Rob Hailstone, analyst at research firm IDC, agrees that it is highly likely virus writers will eventually start using metamorphic viruses. "The virus writers have always tried to outsmart the anti-virus vendors, so it is logical they will enter the race with increasingly complicated weapons," he said.

Graham Cluley, senior technology consultant at anti-virus company Sophos, said although polymorphic viruses are more difficult to analyse than normal viruses, modern anti-virus software has been familiar with them for 10 years.

"The encrypted virus always comes with a decryptor which allows the anti-virus to use the decryption algorithm inside the virus against the virus itself. Modern anti-virus software has been able to do this since the early 1990s," he said.