This file searches for a particular string inside your files. Replace "wso" in line 31 with anything you want and it will search all your files for that string. A list of possible patterns is commented at the top.

find-string.php

<?php
/*
 * POSSIBLE PATTERNS="passthru|shell_exec|system|phpinfo|base64_decode|popen|exec|proc_open|pcntl_exec|python_eval|fopen|fclose|readfile"
 */
ini_set('max_execution_time', '0');
ini_set('set_time_limit', '0');
find_files('.');
function find_files($seed) {
  if(!is_dir($seed)) return false;
	$files = array();
	$dirs = array($seed);
	while(NULL !== ($dir = array_pop($dirs))) {
		if($dh = opendir($dir)) {
			while(false !== ($file = readdir($dh))) {
				if($file == '.' || $file == '..') continue;
				$path = $dir . '/' . $file;
				if(is_dir($path)) {
					$dirs[] = $path;
				}
				else {
					if(preg_match('/^.*\.(php[\d]?|js|txt)$/i', $path)) {
						check_files($path);
					}
				}
			}
			closedir($dh);
		}
	}
}
function check_files($this_file) {
	$str_to_find = 'wso'; // the string(code/text) to search for
	if(!($content = file_get_contents($this_file))) {
		echo("<p>Could not check $this_file</p>\n");
	}
	else {
		if(stristr($content, $str_to_find)) {
			echo("<p>$this_file -> contains $str_to_find</p>\n");
		}
	}
	unset($content);
}
?>