Any person can view the source code for one of your AdSense units simply by examining the source code of a page that you display AdSense on. The vast majority of the time, there is no reason why this should ever cause a problem for you. However, suppose that someone with malicious intent decided to post your AdSense units on a website that does not comply with Google’s policies, such as a pornographic site. Although it wouldn’t benefit the person displaying the ads, it could potentially cause a problem for you. This might lead to a temporary suspension while Google investigates the problem. You can prevent the problem from happening in the first place by creating a whitelist in AdSense with the “Allowed Sites” feature. This restricts your AdSense ads so that they only appear on websites that you specify.
Note that there is a potential downside to creating a website whitelist for AdSense; if many people view your websites through other services such as search engine caches, translation pages and proxy websites, you would lose that potential AdSense income. An alternative to restricting AdSense to only your websites is to set up custom URL channels for your AdSense units, and compare AdSense impressions to Google Analytics page views each day. If you find a major discrepancy between the two, notify Google.