@jiejie
You're not crazy. That's about the same time I started receiving the ads. There is a little box that pops up in the bottom-right-hand corner of my screen. The ads on my computer are for 10010 (China Unicom). I had a hunch it was them, but I decided to rule out the other possibilities first. Scans by various antivirus/malware/adware software detected nothing. I confirmed it was not a new type of advertising by the websites. With that out of the way, I called up China Unicom and I complained about pop-up ads; the representative stated that I had agreed to them in my contract when I signed up for internet service. It must be nice being a monopoly (many neighborhoods in China, including mine, only allow one ISP). At least they didn't deny it like they do every time I call up and complain that I can't access YouTube, Facebook, etc. (Yes, I do realize that they are blocked, but sometimes it's just fun to mess with the system.

) Anyway, they aren't the first ISP to insert ads (search for "Phorm" or "ISP inserting ads"). Hopefully, these bad advertising practices by ISPs will be the next story to go viral on Weibo.
Also, apparently, this has been going on a long time, so maybe we're actually lucky we are only now experiencing it:
- http://www.marc.cn/2010/07/china-uni...ermission.html
- http://news.ichinastock.com/2011/04/...th-pop-up-ads/