During the course, he found a computer virus, one of the first viruses, called the Brain, on his floppy diskette. He started to analyze and develop the vaccine software program. He also uploaded the program, and wrote about it in the magazine "Microsoft", a technical magazine which covers computer programs. He upgraded the vaccine program and introduced the V2, V2 Plus to the public with adding the function which can cure the LBC and Jerusalem viruses. He finally introduced the V3 program, now a very important software program for Korean computer users.