To tackle Adsense Theft, Google has introduced a new feature which lets you whitelist the sites which show your Google Ad. You can specify the whitelist by logging into your Adsense account, and navigating to Adsense Setup > Allowed Site (google.com/adsense/publisher-whitelist-view).
The whitelist doesn’t prevent other sites from showing your Google Ad, but the impression and clicks won’t be count. This prevents inappropriate sites from stealing your Adsense codes and placing it on their site, with the intention of getting you banned out of Adsense.
Not all Adsense publishers are in favor of this feature. Amit Agarwal writes that he’ll leave this feature untouched because a part of his traffic comes from Yahoo/Google cache. By turning on this whitelist, he may be losing a part of his revenues.
I have never been into a situation where my ad code was being used by some malicious site, but I’ll still add my site into the whitelist. It’s pretty hard to figure out, if any other site is showing your Google Ad, so better be safe than sorry.

wrote, on September 12th, 2007
Wow yes, I will definately be using this feature! I can;t see why someone would make money from the cache pageviews. How many people view the cached version of a site? Surely not enough to make any significant revenue from?
wrote, on September 12th, 2007
Matt Arnold: yeah, I agree with you. I didn’t go deeper into Amit’s stats, but I don’t get much P/Vs from cache views!
wrote, on October 11th, 2007
That’s pretty crazy that people would stoop to that low level. I wonder if this happened if Google would automatically delete your account or give a chance to defend yourself.
wrote, on October 12th, 2007
yes its really hard , when someone did this to your adsense account i hope that google make a new rules or make it better for us publisher
wrote, on February 12th, 2008
I’ve had someone do this to me before. I was glad when this feature was implemented.
wrote, on June 13th, 2008
I wasn’t even aware yours ads could be stolen… Thanks for the information!
wrote, on August 18th, 2008
This is definitely a smart way to keep to avoid theft of your adsense. It’s amazing how far some people would go, hey.