Checking and Criteria of Infection
Sorry for not updating here lately but now I will continue what I promised for. Your virus should be judicious in its infection. For example, you might not want to infect COMMAND.COM, since some programs (i.e. the puny FluShot+) check its CRC or checksum on runtime. Perhaps you do not wish to infect the first valid file in the directory. Ambulance Car is an example of such a virus. Regardless, if there is some infection criteria, you should check for it now. Here's example code checking if the last two letters are 'ND', a simple check for COMMAND.COM: cmp word ptr [bp+offset DTA+35], 'DN' ; Reverse word order jz fail_check Every virus has certain characteristics with which you can identify whether a file is infected already. For example, a certain piece of code may always occur in a predictable place. Or perhaps the JMP instruction is always coded in the same manner. Regardless, you s