Author: Yovanny Rodriguez

How to delete a file permanently?

Answer:

If you want to get rid of a file normally you just delete it. But someone else can 
undelete it if the file hasn't been wiped correctly. For security purposes, to 
insure that certain files are permanently gone, the WipeFile procedure writes over 
the data in the file with random characters and then erases it. 

1   procedure WipeFile(FileName: string);
2   var
3     buffer: array[0..4095] of Byte;
4     max, n: LongInt;
5     i: Integer;
6     fs: TFileStream;
7   
8     procedure RandomizeBuffer;
9     var
10      i: Integer;
11    begin
12      for i := Low(buffer) to High(buffer) do
13        buffer[i] := Random(256);
14    end;
15  begin
16    fs := TFilestream.Create(FileName, fmOpenReadWrite or fmShareExclusive);
17    try
18      for i := 1 to 3 do
19      begin
20        RandomizeBuffer;
21        max := fs.Size;
22        fs.Position := 0;
23        while max > 0 do
24        begin
25          if max > SizeOf(buffer) then
26            n := SizeOf(buffer)
27          else
28            n := max;
29          fs.write(Buffer, n);
30          max := max - n;
31        end;
32        FlushFileBuffers(fs.Handle);
33      end;
34    finally
35      fs.Free;
36    end;
37    Deletefile(FileName);
38  end;