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Thanks a lot! I guess I need to self-educate myself a little bit before I implement your suggestions. :))

Another question just jumped out of my mind, suppose I drop those malicious requests, will Google still charge me for those clicks?

Well, maybe one more ENTRY-LEVEL question on the Google Checkout (bu hao yi si), is it possible to use google checkout without a shopping cart? I mean my website is more like a marketing channel rather than an online store. I would like to use Google Checkout as a credit card processing tool. Will I be able to do so? If not, I will not bother to go through the learning materials. :)

Thanks to Ohlalala and anybody who may be able to help me.