China ISP Ad Injection
It appears, that China is doing ISP-level ad-blocking and ad-injection.
Following are screenshots of xahlee.info, of the page: Keyboard Key Switch Mechanisms. Screenshots taken in Hangzhou, China, taken on .
xahlee.info is hosted in USA, and main audience is North American. xahlee.info runs Google Ads, and also amazon.com ads.
In the following screenshots, the square ads on the lower corner is foreign, likely injected by China's ISP.
Articles about ISP-level Ad injection:
[How a banner ad for H＆R Block appeared on apple.com—without Apple's OK. Someone, somewhere is injecting banner ads into webpages on the sly. By Nate Anderson. At http://arstechnica.com/tech-policy/2013/04/how-a-banner-ad-for-hs-ok/ , accessed on 2015-07-24 ]