The IRS uses mainframes, mostly IBM from what I've heard. I don't know of anyone who has sucessfuly written a virus that would run on a mainframe. The next problem would be how to get it on a mainframe and that would be a great problem. Next and probably the most difficult is how do you get your program executed. Going in through an internal reader would require installation specific data and getting a program to run is system state (key 0) is next to impossible without being a system programmer in the specific installation.