title: PHP - Is "include" function secure?
body: <p>I'm using the "include" function (e.x. "include 'header2.php'" or "include 'class.users.php'")
  to add the header or session class in my website. I don't really remember where, but I heard that hackers abuse, somehow, this "include" thing, sending the fake included page or something like that.
  So basically I would like to know what's with that "include" function, how can I protect it, how do they abuse it and if there are better solutions for what I am looking for.</p>
  
  <p>Thanks in advance.</p>