View difference between Paste ID: btXtDW7M and 4nnDAn15

 <!DOCTYPE html>
 <!-- ^ Always define a DOCTYPE - Read more about DOCTYPEs on w3c -->
 <html>
 <head>
 	<title>Vulnerability Scanner</title>
 	<style type="text/css">
 		body {
 			color: #ffffff;
 			text-shadow: 2px 2px #000000;
 			background-color: #282828;
 			font-family: Arial, Helvetica, sans-serif;
 		}
 
 		pre {
 			background-color: #353535;
 			border: solid 1px #505050;
 		}
 
 		input {
 			font-family: Arial, Helvetica, sans-serif;
 		}
 
 		.Button {
 			padding: 5px 10px;
 			background: #303030;
 			border: solid #101010 1px;
 			color: #fff;
 			cursor: pointer;
 			font-weight: bold;
 			border-radius: 5px;
 			-moz-border-radius: 5px;
 			-webkit-border-radius: 5px;
 			text-shadow: 1px 1px #000;
 		}
 
 		.Input {
 			border: solid #101010 1px;
 			color: white;
 			font-weight: bold;
 			padding: 3px;
 			background-color: #252525;
 		}
 	</style>
 </head>
 
 <body>
 	<div align="center">
 		<pre>
              _____   _                  _      _          _                          _         _
             |_   _| | |__     ___      / \    | |   ___  | |__     ___   _ __ ___   (_)  ___  | |_
               | |   | |_ \   / _ \    / _ \   | |  / __| | |_ \   / _ \ | |_ ` _ \  | | / __| | __|
               | |   | | | | |  __/   / ___ \  | | | (__  | | | | |  __/ | | | | | | | | \__ \ | |_
               |_|   |_| |_|  \___|  /_/   \_\ |_|  \___| |_| |_|  \___| |_| |_| |_| |_| |___/  \__|
               Vulnerability Scanner                                              www.hackforums.net
 		</pre>
 
 		<form method="POST" action="">
 			Enter URL : <input type="text" name="url" value="<?php if(isset($_POST['url'])){echo(htmlentities($_POST['url']));}
 			else{echo('http://example.com/index.php?id=1');} ?>" size="75" class="Input" />
 			<input type="submit" name="submit" value="Scan" class="Button" />
 		</form>
 
 		<br />
 <?php
 
 //Coded by The Alchemist
 //Styled and modified by ande
 //Thanks again ande
 
 class VulnScanner {
    // ^   ^    CamelCase.
 
 	// This is a good example, you should NEVER store data in the class that the user is going to want to change. Make a config file, use an XML file etc are all great alternatives.
 	protected $types = array(
 		'sql' => array('errors' => array("mysql_", "You have an error in your SQL syntax", "SQL Error", "Database Error", "supplied argument is not a valid MySQL result resource"),'vulnerability' => array("'",'"')),
 		'rfi' => array('errors' => array("Welcome to Facebook - Log In, Sign Up or Learn More", "failed to open stream: No such file or directory"), 'vulnerability' => array("http://www.facebook.com")),
 		'lfi' => array('errors' => array("root:x:0:0:root:", "failed to open stream: No such file or directory"), 'vulnerability' => array("../etc/passwd",
 					   "../../etc/passwd",
 					   "../../../etc/passwd",
 					   "../../../../etc/passwd",
 					   "../../../../../etc/passwd",
 					   "../../../../../../etc/passwd")),
 		'xss' => array('errors' => array("<img src=\"http://owned.com\"/>"), 'vulnerability' => array("'\"/><img src=\"http://owned.com\"/>"))
 	);
 
 	public function __construct() {
 		// This is good too. We want the user to know that he can't use it before it spits out 2349234982 errors.
-		if(extension_loaded('curl')) {
+		if(!extension_loaded('curl')) {
 			throw new Exception('cURL must be enabled');
 		}
 	}
 	public function isValid($link) {
 					// ^ You should try loosely following PSR standards (I say loosely because PSR standards are far too strict, even for me.) -- This example is known as "camelCase"
 		// Personally, I don't think you even need a function for this. But, this is much cleaner. Research "PHP Ternary" (I say PHP ternary because PHP ternary is different than literally every other langauage)
 		return filter_var($link, FILTER_VALIDATE_URL) ? (strstr($link, "=") ? true : false) : false;
 	}
 
 
 	private function getContents($link, $userAgent = 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0') {
 					 // Again, camelCase
 		$ch = curl_init();
 		curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
 		curl_setopt($ch, CURLOPT_VERBOSE, true);
 		curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
 		curl_setopt($ch, CURLOPT_USERAGENT, $userAgent);
 											// Beats storing an unchangeable variable. If it's something that that user may want to change without much hassle, put it in the argument list@
 		curl_setopt($ch, CURLOPT_URL,$link);
 		$result = curl_exec($ch);
 		return $result;
 	}
 
 	private function errorCheck($url, $addtourl, $errorar) {
 								// Even if you are documenting your functions, all variable names should be clear. This doesn't mean really long names, but give it short and simple meanings.
 		foreach($addtourl as $val) {
 			$link = $url.$val;
 			$contents = $this->getcontents($link);
 			foreach($errorar as $err) {
 				if(strstr($contents, $err)) {
 					return true;
 				}
 			}
 		}
 		return false;
 	}
 
 	// See? Much cleaner! Still lots more do to though...
 	public function isVulnerable($url, $type = 'sql') {
 		if(!isset($this->types[$type])) {
 			throw new Exception('Invalid type: ' . $type);
 		} else {
 			if($this->errorCheck($link, $this->$type['vulnerability'], $this->$type['errors']) ) {
 				echo htmlentities($link) . " <span style=\"color: red;\">might</span> be vulnerable to SQL Injection.<br />";
 			} else {
 				echo htmlentities($link) . " is probably <span style=\"color: red;\">NOT</span> vulnerable to SQL Injection.<br />";
 			}
 		}
 	}
 
 	public function isSQLVulnerable($link) {
 		$orig = $link; // Why'd you do that? VulnScanner::errorcheck did not reference the variable, so making an "original value" variable is redundant.
 		if($this->errorcheck($orig,$this->sql,$this->sqlerrors))
 			echo htmlentities($orig) ." <span style=\"color: red;\">might</span> be vulnerable to SQL Injection.<br />";
 		else
 			echo htmlentities($orig) ." is probably <span style=\"color: red;\">NOT</span> vulnerable to SQL Injection.<br />";
 	}
 }
 
 
 
 if(isset($_POST['url']) && isset($_POST['submit'])) {
 	$obj = new VulnScanner();
 	$link = $_POST['url'];
 	if($obj->isValid($link)) {
 		$obj->isVulnerable($link, 'sql'); // ta-da!
 	} else {
 		echo "<span style=\"color: red;\">". htmlentities($link) ." is not a valid link.</span>";
 	}
 }
 ?>
 </body>
 </html>