I have been seeing reports of Google banning and disabling AdSense accounts due to using a Firefox plugin named Tamper Data. Tamper Data allows people to view and modify HTTP/HTTPS headers and post parameters, which can be helpful, but also used for evil.
The emails being sent to these publishers read:
During a recent review of your account, our specialists found that tamper data was used to modify the country listed in your account. Changing your address in this manner is a violation of our policy guidelines.
In summary, certain countries are not allowed to sign up for AdSense so people fake where they are from. I am not sure why people would use this technique when they are in an approved location, unless I am missing something?