Missing page impressions?

when comparing adsense vs. AW Stats

[javahava]

We have four sites on adsense. With 3 of the sites, the page impressions shown in adsense is usually about 10% less of the page impressions we see in AW Stats (which makes sense, given PSAs, etc.). In one site, though, the adsense impressions are more than 60% less than the page impressions we see in AW stats (just noticed this). Has anyone else encountered such large discrepancies?

we've rechecked our adsense code and it seems to be correct. not sure what might be going-on, if AW stats might be counting bot traffic as page impressions. what do you guys think? thanks!

[The Contractor]

Site rippers/downloaders, bots, people with JavaScript turned off, and quite a few other things can cause a dramatic difference.

Also, there seems to be a surge of people buying traffic from a few places that guarantee to send visitors and they are nothing more than clickbots being run behind rotating proxies....of course the people buying those services don't know that. From what I have seen these are not programmed to parse JavaScript.

[frox]

My sites are showing this quite constantly.

By careful examinations of raw logs, I saw there are "spiders" that G recognizes as "bots" but AWstat does not.

Many "grabber" programs (programs that methodically download all your sites) have the option to se the HTTP agent, so if AWstat relies on that those pegeviews will be conted in AWStat but not in Adsense, therefore the difference.

[javahava]

Interesting - thank you. On a related note: if you suspect your site content is being grabbed (like you mentioned), what steps do you typically take to prevent further abuse, etc.?

[frox]

I have a (custom) script that counts accesses by IP in the last X minutes.

If they are over a certain limit, and do not fall in a known list of "good" spiders, I start returning garbage :-)