title: is it dangerous to zip/unzip unknown uploaded files on server that may contain anything? even viruses?
body: <p>i am trying to implement a user system (php, apache) where the user can upload several files and download a zipped version of them. (or uploading a zipped file and download the uncompressed files).</p>
  
  <p><strong>question:</strong> is there any risk to zip/unzip those unknown files?
  in other words, are unix/php zip/unzip operations treat files as text only or some execution can occur?</p>
  
  <p><strong>This question is relevant to all compression methods, zip is just an example.</strong></p>
  
  <p><strong>EDIT:</strong> @Alex Brown AND @Parallelis wrote 2 risks so obviously it is not safe.
  any one can post a short explanation on how to implement a safe compress/uncompress of unknown files?</p>