Description:
------------
In the documentation of system(), exec(), shell_exec(), popen(), passthru() and other external proces execution function there should be the following notes:
1. All these functions does not execute the requested process directly: they execute a shell (cmd.exe ? bash ? which criteria is used ? %COMSPEC% in windows ?).
2. Executing the standard CMD.EXE in windows is not possible when running as a non administrator user, so these function will fail in a standard IIS environment, where the current PHP script is executed as ISUR_MACHINENAME
3. The only secure way to execute a process in windows bypassing cmd.exe, is to use the proc_open() function with the option "bypass_shell"

Reproduce code:
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---
From manual page: function.system
---
<?php
  passthru("ping www.hp.com");
?>

Expected result:
----------------
A typical ping output

Actual result:
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Warning: passthru() [function.passthru]: Unable to fork [ping www.hp.com] in C:\Inetpub\wwwroot\prova.php on line 2