Cool tool that generates a file containing the EICAR test virus.  File's contents are completely harmless, but should still set off your anti-virus system.  Very useful for testing  your AV detection system and checking its response.  Since the test virus itself is normally blocked, here's a handy way to simply generate it whenever you want.

This is an improved version of the tool originally created by Didier Stevens.  It obscures the virus payload in the binary image to prevent detection, but also requires the "-c" switch in the command line to produce the file.  I've found some AV systems now test run executables in a sandbox, and if a trojan pops out there're irradicated just like the payload.  This caused EICARgen to be blocked.