How to remove web viruses in php_PHP tutorial

Class clear_virus{
public $index ='b.html';
public $filepath =array('b.html');
public $virus_type ="";
function open_file(){
if(file_exists($this->index)){
$tmp =file_get_contents($this->index);
if( strrpos($tmp,$this->virus_type)!== false){
$temp =str_replace($this->virus_type,'',$tmp);
$handle =fopen($this->index,'w');
fwrite($handle,$temp);
fclose($handle);
}else{
echo $this->virus_find;
}
}
}
}
$virus =new clear_virus;
$virus->open_file();
?>
清除script 病毒