EICAR is a short 68-byte COM file that is detected by anti-virus programs as a virus, but is actually NOT “VIRAL” at all. When executed it just displays a message and returns control to the host program.
Some time ago researchers from several anti-virus companies were asked by users to develop a way to demonstrate what would happen in case of a real virus attack; a sort of simulation of which messages anti-virus programs will display and what actions will be recommended to perform, e.t.c.
After some time and thought toward how to best satisfy the request, the anti-virus researchers decided to release some virus-simulators that would be some harmless file that does nothing but display a message(s) and then exits to DOS (host OS). It was decided that this file could contain only ASCII characters so that users could type it or copy it from a User Guide. As a result the COM file looks as follows: