$re = '/microsoft_?[0-9]+_?[a-z]+\.(zip|exe|xls|xlsm)/i';
$str = 'MICROSOFT_0383760007_contact.exe
MICROSOFT0383760007_contacto.zip
MICROSOFT_0383760007contacto.zip
MICROSOFT0383760007contacto.zip
^[Mm][Ii][Cc][Rr][Oo][Ss][Oo][Ff][Tt][_][0-9]+[_][a-z]+.zip$
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php