Called W64.Rugrat.3344, the virus is a direct action infector, which means that it quits the system memory once it has executed. The virus infects.... what are known as IA64 Windows Portal Executable files.
Although the virus is not capable of infecting a 32 bit Portable Executable file, or indeed of running on a 32 bit Microsoft Windows platform natively, it is possible to run it on a 32 bit machine using a 64 bit emulator.
Although the virus is rated by Symantec as being low risk, and is more of a proof of concept than anything else, it is worrying that 64 bit viruses for Microsoft Windows are already emerging. Symantec's latest virus definitions will remove the virus, and other virus companies will follow suit shortly we would imagine. Full virus information and removal instructions are available here.