Oops, I’ve misunderstand the syntax of user agent tag. The following code can exclude most bot hits, with also Baidu search and Yahoo search.

if ( (stristr($useragent, "bot") === TRUE) || (stristr($useragent, "spider") === TRUE) || (stristr($useragent, "crawler") === TRUE) || (stristr($useragent, "baidu") === TRUE) || (stristr($useragent, "Yahoo! Slurp") === TRUE) )
$checkval = TRUE;

So replace it with the old one. If you are new, add this below these two lines (around line 377) in wp-content/plugins/counterize.php:
$excludelist=get_option(‘counterize_excluded’);
$checkval = strpos($excludelist, $remoteaddr);

Old version:
Exclude Bot Hits from Counterize

Counterize 另一個可以修改的地方是它會計算 Bot⁽¹⁾ 的來訪。剛才看見作者留言板上有人說要不停加入不同 Bot 的 IP 到 Exclusion List 頗為麻煩，但是其實有捷徑的。因為多數 Bot 的 Useragent 裏都會有「bot」這個字串，所以可以靠檢查 Useragent 來減去 Bot count。
(Full content for English explaination)
» Read more: Exclude Bot Hits from Counterize

雖然的確是要考試，但又忍不住手去改程式 (天啊，我是否真的應轉讀 CS？) 經過試用 SESSION 及 COOKIES 的屢戰屢敗後，結果用了原始的方法：開個 TXT 檔來記錄最近的訪客 IP 及其時間。因為可能其他地方的網友亦有這種需要，所以下文用英文，請見諒。

Introduction:
Counterize is a WordPress Plugin, as a page-hit-counter. It counts every page hit, and provides many useful functions, such as getting total hit, hit from current user, today’s hit etc. But one thing is that it is not based on SESSION, and can’t ignore multiple hits from a recent user. I’ve done a little modification to archieve this. If you need this function, just do the same to your wordpress.
» Read more: Ignore Multiple Hits Modification to Counterize