WriteString bug???

I am writing to a file.

Here is the code:

fileout = WriteFile(file$)				
WriteString fileout,"Hello"
WriteInt fileout,TILE_WIDTH
WriteInt fileout,TILE_HEIGHT
CloseFile(fileout)

Everything seems to work but when I open the file into a hex editor, I notice it puts 4 bytes in front of "Hello".
Why is that?

Thanks

cb