Purge is standalone version of well-known Codeigniter xss_clean. just copy and pasted from CI to make it work out of box. Purge::xss_clean($data);

Purge.php

<?php


Class Purge {

    static $instance   = false;
    /**
     * IP address of the current user
     *
     * @var string
     */
    var $ip_address = FALSE;
    /**
     * user agent (web browser) being used by the current user
     *
     * @var string
     */
    var $user_agent = FALSE;
    /**
     * List of all HTTP request headers
     *
     * @var array
     */
    protected $headers = array();
    /**
     * List of never allowed strings
     *
     * @var array
     * @access protected
     */
    /**
     * Random Hash for protecting URLs
     *
     * @var string
     * @access protected
     */
    static $_xss_hash = '';

    static protected $_never_allowed_str = array(
        'document.cookie'   => '[removed]',
        'document.write'    => '[removed]',
        '.parentNode'       => '[removed]',
        '.innerHTML'        => '[removed]',
        'window.location'   => '[removed]',
        '-moz-binding'      => '[removed]',
        '<!--'              => '&lt;!--',
        '-->'               => '--&gt;',
        '<![CDATA['         => '&lt;![CDATA[',
        '<comment>'         => '&lt;comment&gt;'
    );

    /* never allowed, regex replacement */
    /**
     * List of never allowed regex replacement
     *
     * @var array
     * @access protected
     */
    static protected $_never_allowed_regex = array(
        'javascript\s*:',
        'expression\s*(\(|&\#40;)', // CSS and IE
        'vbscript\s*:', // IE, surprise!
        'Redirect\s+302',
        "([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?\\1?"
    );

    public function &init()
    {
        if (self::$instance === false) {
            self::$instance = new self();
        }

        return self::$instance;
    }


    /**
     * Fetch from array
     *
     * This is a helper function to retrieve values from global arrays
     *
     * @param   array   $array
     * @param   string  $index
     * @return  string
     */
    private function _fetch_from_array(&$array, $index='')
    {
        if ( ! isset($array[$index]))
        {
            return FALSE;
        }

        return self::xss_clean($array[$index]);
    }

    /**
    * Fetch an item from the GET array
    *
    * @param    string  $index
    * @return   string
    */
    public function get($index = NULL)
    {
        // Check if a field has been provided
        if ($index === NULL AND ! empty($_GET))
        {
            $get = array();

            // loop through the full _GET array
            foreach (array_keys($_GET) as $key)
            {
                $get[$key] = self::_fetch_from_array($_GET, $key);
            }
            return $get;
        }

        return self::_fetch_from_array($_GET, $index);
    }

    /**
    * Fetch an item from the POST array
    *
    * @param    string  $string
    * @return   string
    */
    public function post($index = NULL)
    {
        // Check if a field has been provided
        if ($index === NULL AND ! empty($_POST))
        {
            $post = array();

            // Loop through the full _POST array and return it
            foreach (array_keys($_POST) as $key)
            {
                $post[$key] = self::_fetch_from_array($_POST, $key);
            }
            return $post;
        }

        return self::_fetch_from_array($_POST, $index);
    }

    /**
    * Fetch an item from either the GET array or the POST
    *
    * @param    string  $index
    * @return   string
    */
    public function get_post($index = '')
    {
        if ( ! isset($_POST[$index]) )
        {
            return self::get($index);
        }
        else
        {
            return self::post($index);
        }
    }

    /**
    * Fetch an item from the COOKIE array
    *
    * @param    string  $index
    * @return   string
    */
    public function cookie($index = '')
    {
        return self::_fetch_from_array($_COOKIE, $index);
    }

    /**
    * Fetch an item from the SERVER array
    *
    * @param    string  $index
    * @return   string
    */
    public function server($index = '')
    {
        return self::_fetch_from_array($_SERVER, $index);
    }

    /**
    * User Agent
    *
    * @return   string
    */
    public function user_agent()
    {
        if (self::$user_agent !== FALSE)
        {
            return self::$user_agent;
        }

        self::$user_agent = ( ! isset($_SERVER['HTTP_USER_AGENT'])) ? FALSE : $_SERVER['HTTP_USER_AGENT'];

        return self::$user_agent;
    }

    /**
    * Sanitize Globals
    *
    * This function does the following:
    *
    * Unsets $_GET data (if query strings are not enabled)
    *
    * Unsets all globals if register_globals is enabled
    *
    * Standardizes newline characters to \n
    *
    * @access   private
    * @return   void
    */
    function _sanitize_globals()
    {
        // Clean $_GET Data
        if (is_array($_GET) AND count($_GET) > 0)
        {
            foreach ($_GET as $key => $val)
            {
                $_GET[self::_clean_input_keys($key)] = self::_clean_input_data($val);
            }
        }

        // Clean $_POST Data
        if (is_array($_POST) AND count($_POST) > 0)
        {
            foreach ($_POST as $key => $val)
            {
                $_POST[self::_clean_input_keys($key)] = self::_clean_input_data($val);
            }
        }

        // Sanitize PHP_SELF
        $_SERVER['PHP_SELF'] = strip_tags($_SERVER['PHP_SELF']);
    }

    /**
     * XSS Clean
     *
     * Sanitizes data so that Cross Site Scripting Hacks can be
     * prevented.  This function does a fair amount of work but
     * it is extremely thorough, designed to prevent even the
     * most obscure XSS attempts.  Nothing is ever 100% foolproof,
     * of course, but I haven't been able to get anything passed
     * the filter.
     *
     * Note: This function should only be used to deal with data
     * upon submission.  It's not something that should
     * be used for general runtime processing.
     *
     * This function was based in part on some code and ideas I
     * got from Bitflux: http://channel.bitflux.ch/wiki/XSS_Prevention
     *
     * To help develop this script I used this great list of
     * vulnerabilities along with a few other hacks I've
     * harvested from examining vulnerabilities in other programs:
     * http://ha.ckers.org/xss.html
     *
     * @param   mixed   string or array
     * @param   bool
     * @return  string
     */
    public function xss_clean($str, $is_image = FALSE)
    {
        if (self::$instance === false) {
            self::init();
        }

        /*
         * Is the string an array?
         *
         */
        if (is_array($str))
        {
            while (list($key) = each($str))
            {
                $str[$key] = self::xss_clean($str[$key]);
            }

            return $str;
        }

        /*
         * Remove Invisible Characters
         */
        $str = self::remove_invisible_characters($str);

        // Validate Entities in URLs
        $str = self::_validate_entities($str);

        /*
         * URL Decode
         *
         * Just in case stuff like this is submitted:
         *
         * <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>
         *
         * Note: Use rawurldecode() so it does not remove plus signs
         *
         */
        $str = rawurldecode($str);

        /*
         * Convert character entities to ASCII
         *
         * This permits our tests below to work reliably.
         * We only convert entities that are within tags since
         * these are the ones that will pose security problems.
         *
         */

        $str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", array(self::$instance, '_convert_attribute'), $str);

        $str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", array(self::$instance, '_decode_entity'), $str);

        /*
         * Remove Invisible Characters Again!
         */
        $str = self::remove_invisible_characters($str);

        /*
         * Convert all tabs to spaces
         *
         * This prevents strings like this: ja  vascript
         * NOTE: we deal with spaces between characters later.
         * NOTE: preg_replace was found to be amazingly slow here on
         * large blocks of data, so we use str_replace.
         */

        if (strpos($str, "\t") !== FALSE)
        {
            $str = str_replace("\t", ' ', $str);
        }

        /*
         * Capture converted string for later comparison
         */
        $converted_string = $str;

        // Remove Strings that are never allowed
        $str = self::_do_never_allowed($str);

        /*
         * Makes PHP tags safe
         *
         * Note: XML tags are inadvertently replaced too:
         *
         * <?xml
         *
         * But it doesn't seem to pose a problem.
         */
        if ($is_image === TRUE)
        {
            // Images have a tendency to have the PHP short opening and
            // closing tags every so often so we skip those and only
            // do the long opening tags.
            $str = preg_replace('/<\?(php)/i', "&lt;?\\1", $str);
        }
        else
        {
            $str = str_replace(array('<?', '?'.'>'),  array('&lt;?', '?&gt;'), $str);
        }

        /*
         * Compact any exploded words
         *
         * This corrects words like:  j a v a s c r i p t
         * These words are compacted back to their correct state.
         */
        $words = array(
            'javascript', 'expression', 'vbscript', 'script', 'base64',
            'applet', 'alert', 'document', 'write', 'cookie', 'window'
        );

        foreach ($words as $word)
        {
            $temp = '';

            for ($i = 0, $wordlen = strlen($word); $i < $wordlen; $i++)
            {
                $temp .= substr($word, $i, 1)."\s*";
            }

            // We only want to do this when it is followed by a non-word character
            // That way valid stuff like "dealer to" does not become "dealerto"
            $str = preg_replace_callback('#('.substr($temp, 0, -3).')(\W)#is', array(self::$instance, '_compact_exploded_words'), $str);
        }

        /*
         * Remove disallowed Javascript in links or img tags
         * We used to do some version comparisons and use of stripos for PHP5,
         * but it is dog slow compared to these simplified non-capturing
         * preg_match(), especially if the pattern exists in the string
         */
        do
        {
            $original = $str;

            if (preg_match("/<a/i", $str))
            {
                $str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", array(self::$instance, '_js_link_removal'), $str);
            }

            if (preg_match("/<img/i", $str))
            {
                $str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?>|$)#si", array(self::$instance, '_js_img_removal'), $str);
            }

            if (preg_match("/script/i", $str) OR preg_match("/xss/i", $str))
            {
                $str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', $str);
            }
        }
        while($original != $str);

        unset($original);

        // Remove evil attributes such as style, onclick and xmlns
        $str = self::_remove_evil_attributes($str, $is_image);

        /*
         * Sanitize naughty HTML elements
         *
         * If a tag containing any of the words in the list
         * below is found, the tag gets converted to entities.
         *
         * So this: <blink>
         * Becomes: &lt;blink&gt;
         */
        $naughty = 'alert|applet|audio|basefont|base|behavior|bgsound|blink|body|embed|expression|form|frameset|frame|head|html|ilayer|iframe|input|isindex|layer|link|meta|object|plaintext|style|script|textarea|title|video|xml|xss';
        $str = preg_replace_callback('#<(/*\s*)('.$naughty.')([^><]*)([><]*)#is', array(self::$instance, '_sanitize_naughty_html'), $str);

        /*
         * Sanitize naughty scripting elements
         *
         * Similar to above, only instead of looking for
         * tags it looks for PHP and JavaScript commands
         * that are disallowed.  Rather than removing the
         * code, it simply converts the parenthesis to entities
         * rendering the code un-executable.
         *
         * For example: eval('some code')
         * Becomes:     eval&#40;'some code'&#41;
         */
        $str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', "\\1\\2&#40;\\3&#41;", $str);


        // Final clean up
        // This adds a bit of extra precaution in case
        // something got through the above filters
        $str = self::_do_never_allowed($str);

        /*
         * Images are Handled in a Special Way
         * - Essentially, we want to know that after all of the character
         * conversion is done whether any unwanted, likely XSS, code was found.
         * If not, we return TRUE, as the image is clean.
         * However, if the string post-conversion does not matched the
         * string post-removal of XSS, then it fails, as there was unwanted XSS
         * code found and removed/changed during processing.
         */

        if ($is_image === TRUE)
        {
            return ($str == $converted_string) ? TRUE: FALSE;
        }

        return $str;
    }

    /**
     * Random Hash for protecting URLs
     *
     * @return  string
     */
    public function xss_hash()
    {
        mt_srand();
        self::$_xss_hash = md5(time() + mt_rand(0, 1999999999));

        return self::$_xss_hash;
    }

    /**
     * Remove Invisible Characters
     *
     * This prevents sandwiching null characters
     * between ascii characters, like Java\0script.
     *
     * @access  public
     * @param   string
     * @return  string
     */
    public function remove_invisible_characters($str, $url_encoded = TRUE)
    {
        $non_displayables = array();

        // every control character except newline (dec 10)
        // carriage return (dec 13), and horizontal tab (dec 09)

        if ($url_encoded)
        {
            $non_displayables[] = '/%0[0-8bcef]/';  // url encoded 00-08, 11, 12, 14, 15
            $non_displayables[] = '/%1[0-9a-f]/';   // url encoded 16-31
        }

        $non_displayables[] = '/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]+/S';   // 00-08, 11, 12, 14-31, 127

        do
        {
            $str = preg_replace($non_displayables, '', $str, -1, $count);
        }
        while ($count);

        return $str;
    }

    /**
     * Validate URL entities
     *
     * Called by xss_clean()
     *
     * @param   string
     * @return  string
     */
    protected function _validate_entities($str)
    {
        /*
         * Protect GET variables in URLs
         */

         // 901119URL5918AMP18930PROTECT8198

        $str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', self::xss_hash()."\\1=\\2", $str);

        /*
         * Validate standard character entities
         *
         * Add a semicolon if missing.  We do this to enable
         * the conversion of entities to ASCII later.
         *
         */
        $str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", $str);

        /*
         * Validate UTF16 two byte encoding (x00)
         *
         * Just as above, adds a semicolon if missing.
         *
         */
        $str = preg_replace('#(&\#x?)([0-9A-F]+);?#i',"\\1\\2;",$str);

        /*
         * Un-Protect GET variables in URLs
         */
        $str = str_replace(self::xss_hash(), '&', $str);

        return $str;
    }

    /**
     * Attribute Conversion
     *
     * Used as a callback for XSS Clean
     *
     * @param   array
     * @return  string
     */
    protected function _convert_attribute($match)
    {
        return str_replace(array('>', '<', '\\'), array('&gt;', '&lt;', '\\\\'), $match[0]);
    }

    /**
     * HTML Entity Decode Callback
     *
     * Used as a callback for XSS Clean
     *
     * @param   array
     * @return  string
     */
    protected function _decode_entity($match)
    {
        return self::entity_decode($match[0], 'UTF-8');
    }

    /**
     * HTML Entities Decode
     *
     * This function is a replacement for html_entity_decode()
     *
     * The reason we are not using html_entity_decode() by itself is because
     * while it is not technically correct to leave out the semicolon
     * at the end of an entity most browsers will still interpret the entity
     * correctly.  html_entity_decode() does not convert entities without
     * semicolons, so we are left with our own little solution here. Bummer.
     *
     * @param   string
     * @param   string
     * @return  string
     */
    public function entity_decode($str, $charset='UTF-8')
    {
        if (stristr($str, '&') === FALSE)
        {
            return $str;
        }

        $str = html_entity_decode($str, ENT_COMPAT, $charset);
        $str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', $str);
        return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str);
    }

    /**
     * Do Never Allowed
     *
     * A utility function for xss_clean()
     *
     * @param   string
     * @return  string
     */
    protected function _do_never_allowed($str)
    {
        $str = str_replace(array_keys(self::$_never_allowed_str), self::$_never_allowed_str, $str);

        foreach (self::$_never_allowed_regex as $regex)
        {
            $str = preg_replace('#'.$regex.'#is', '[removed]', $str);
        }

        return $str;
    }

    /**
     * Compact Exploded Words
     *
     * Callback function for xss_clean() to remove whitespace from
     * things like j a v a s c r i p t
     *
     * @param   type
     * @return  type
     */
    protected function _compact_exploded_words($matches)
    {
        return preg_replace('/\s+/s', '', $matches[1]).$matches[2];
    }

    /**
     * Sanitize Naughty HTML
     *
     * Callback function for xss_clean() to remove naughty HTML elements
     *
     * @param   array
     * @return  string
     */
    protected function _sanitize_naughty_html($matches)
    {
        // encode opening brace
        $str = '&lt;'.$matches[1].$matches[2].$matches[3];

        // encode captured opening or closing brace to prevent recursive vectors
        $str .= str_replace(array('>', '<'), array('&gt;', '&lt;'),
                            $matches[4]);

        return $str;
    }

    /**
     * JS Link Removal
     *
     * Callback function for xss_clean() to sanitize links
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on link-heavy strings
     *
     * @param   array
     * @return  string
     */
    protected function _js_link_removal($match)
    {
        return str_replace(
            $match[1],
            preg_replace(
                '#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|data\s*:)#si',
                '',
                self::_filter_attributes(str_replace(array('<', '>'), '', $match[1]))
            ),
            $match[0]
        );
    }

    /**
     * JS Image Removal
     *
     * Callback function for xss_clean() to sanitize image tags
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on image tag heavy strings
     *
     * @param   array
     * @return  string
     */
    protected function _js_img_removal($match)
    {
        return str_replace(
            $match[1],
            preg_replace(
                '#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si',
                '',
                self::_filter_attributes(str_replace(array('<', '>'), '', $match[1]))
            ),
            $match[0]
        );
    }

    /**
     * Filter Attributes
     *
     * Filters tag attributes for consistency and safety
     *
     * @param   string
     * @return  string
     */
    protected function _filter_attributes($str)
    {
        $out = '';

        if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches))
        {
            foreach ($matches[0] as $match)
            {
                $out .= preg_replace("#/\*.*?\*/#s", '', $match);
            }
        }

        return $out;
    }

    /*
     * Remove Evil HTML Attributes (like evenhandlers and style)
     *
     * It removes the evil attribute and either:
     *  - Everything up until a space
     *      For example, everything between the pipes:
     *      <a |style=document.write('hello');alert('world');| class=link>
     *  - Everything inside the quotes
     *      For example, everything between the pipes:
     *      <a |style="document.write('hello'); alert('world');"| class="link">
     *
     * @param string $str The string to check
     * @param boolean $is_image TRUE if this is an image
     * @return string The string with the evil attributes removed
     */
    protected function _remove_evil_attributes($str, $is_image)
    {
        // All javascript event handlers (e.g. onload, onclick, onmouseover), style, and xmlns
        $evil_attributes = array('on\w*', 'style', 'xmlns', 'formaction');

        if ($is_image === TRUE)
        {
            /*
             * Adobe Photoshop puts XML metadata into JFIF images,
             * including namespacing, so we have to allow this for images.
             */
            unset($evil_attributes[array_search('xmlns', $evil_attributes)]);
        }

        do {
            $count = 0;
            $attribs = array();

            // find occurrences of illegal attribute strings without quotes
            preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*([^\s>]*)/is', $str, $matches, PREG_SET_ORDER);

            foreach ($matches as $attr)
            {

                $attribs[] = preg_quote($attr[0], '/');
            }

            // find occurrences of illegal attribute strings with quotes (042 and 047 are octal quotes)
            preg_match_all("/(".implode('|', $evil_attributes).")\s*=\s*(\042|\047)([^\\2]*?)(\\2)/is",  $str, $matches, PREG_SET_ORDER);

            foreach ($matches as $attr)
            {
                $attribs[] = preg_quote($attr[0], '/');
            }

            // replace illegal attribute strings that are inside an html tag
            if (count($attribs) > 0)
            {
                $str = preg_replace("/<(\/?[^><]+?)([^A-Za-z<>\-])(.*?)(".implode('|', $attribs).")(.*?)([\s><])([><]*)/i", '<$1 $3$5$6$7', $str, -1, $count);
            }

        } while ($count);

        return $str;
    }

    /**
     * Is ajax Request?
     *
     * Test to see if a request contains the HTTP_X_REQUESTED_WITH header
     *
     * @return  boolean
     */
    public function is_ajax_request()
    {
        return (self::server('HTTP_X_REQUESTED_WITH') === 'XMLHttpRequest');
    }


    /**
     * Is cli Request?
     *
     * Test to see if a request was made from the command line
     *
     * @return  bool
     */
    public function is_cli_request()
    {
        return (php_sapi_name() === 'cli' OR defined('STDIN'));
    }
}

Purge::xss_clean($data);