Has anyone else experienced the following and/or can you explain what's going on? Thanks in advance for the information/help.

About once/ week I get a slew of 404 errors in my weblog that appear to be someone trying to hit one of the landing pages I have set up for my Google AdWords campaign. In a matter of minutes I'll receive 200+ of these errors, all hitting the same landing page with a string of parameters tacked on to the end that don't mean anything to my site (but probably do to Google?). On the days that these errors occur, my click through charges are much lower than the number of errors, so it's not someone clicking on a legitimate ad and getting a bad page. Here's a sample of what I'm seeing in the weblog:

82.159.6.26 - - [29/Jun/2005:04:26:03 -0700] "GET /resources/ga9/index.html&sa=l&ai=BCi67JYXCQvGwC4ziRdnPwBaMheUJ7qjzpwH-9-iFBdCGAxABGAFApBVImDlQs_m4oAWYAe9LoAG2zIv-A8gBAQ&num=1 HTTP/1.1" 404 16231 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" "www.mysite.com"
82.159.6.26 - - [29/Jun/2005:04:28:09 -0700] "GET /resources/ga9/index.html&sa=l&ai=B7QWhNIXCQqSSOKziRPb17TKMheUJqqnzpwH-9-iFBdCGAxABGAFApBVImDlQs_m4oAWQAQmYAe9LoAG2zIv-A8gBAQ&num=1 HTTP/1.1" 404 16231 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" "www.mysite.com"
82.159.6.26 - - [29/Jun/2005:04:28:27 -0700] "GET /resources/ga9/index.html&sa=l&ai=BVlHdNoXCQu-mNLyKRevikSiMheUJqqnzpwH-9-iFBdCGAxABGAFApBVImDlQs_m4oAWQAQiYAe9LoAG2zIv-A8gBAQ&num=1 HTTP/1.1" 404 16231 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" "www.mysite.com"
82.159.6.26 - - [29/Jun/2005:04:28:27 -0700] "GET /resources/ga9/index.html&sa=l&ai=BqLewN4XCQqb6G7qmReyphEmMheUJqqnzpwH-9-iFBdCGAxABGAFApBVImDlQs_m4oAWQAQeYAe9LoAG2zIv-A8gBAQ&num=1 HTTP/1.1" 404 16231 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" "www.mysite.com"
82.159.6.26 - - [29/Jun/2005:04:28:28 -0700] "GET /resources/ga9/index.html&sa=l&ai=ByE-BOIXCQoWSEIreRPPbhBuMheUJ7qjzpwH-9-iFBdCGAxABGAFApBVImDlQs_m4oAWQAQaYAe9LoAG2zIv-A8gBAQ&num=1 HTTP/1.1" 404 16231 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" "www.mysite.com"

Any ideas what's going on here? I'm perplexed...

I think it's an example of someone trying clickfraud - either trying to up your costs or make money on adsense - but being successfully filtered by Google (so you're not charged/shown the fraud clicks).

Just my guess. I thought I'd toss my two pence in since I'm not often in this corner of the forums and no one else seemed to be biting.

That's what I think, too, but I haven't been able to prove nor have I been able to couch the question to Google support in such a way that will get them to help.

Thanks for the response.