[PHP] File upload

[Boget, Chris]

>From the manual:

"Handling file uploads Uploading multiple files  
  
Common Pitfalls

Not validating which file you operate on may mean that users 
can access sensitive information in other directories. "


What is meant by the above?  How would you "validate" that
you weren't operating on the wrong file?  As far as I know, 
PHP puts the file in whatever directory you specify and that
is where you would access the file... how could someone make
it so they access information elsewhere?

Chris