The Great Firewall also uses page scanning to intercept content it finds illegal. Say, if you visit a website, the filtration system will immedaitely begin scanning the content on the page. If it finds it acceptable, you'll be able to stay on. If not, you may experience down times from anywhere between a few minutes or an hour. If you keep trying to visit an "unacceptable site," may be reported to Chinese authorities.
So, it Shouldn't Come as a Surprise that Big Brother is Always Watching