This test virus was developed by the European Institute for Computer Anti-Virus Research (EICAR) to provide an easy (and safe!) way to test whether your anti-virus software is working, and see how it reacts when a virus is detected. It is supported by most leading vendors, such as IBM, McAfee, Sophos, and Symantec/Norton.

http://www.rexswain.com/eicar.html