Yesterday, while suddenly exchanging links, I found that the link was clearly added, but it couldn't be detected by tools. Checking the webpage showed that the link was indeed there, leaving me utterly confused. Later, someone even scolded me, saying that the link exchanged in the morning had been secretly deleted by evening, which left me extremely frustrated!
Analyzing the cause, when using a webmaster tool to simulate a search engine, the returned source file simply said "To access this page, your browser needs to support JavaScript." Ah, no wonder the friendly link couldn't be detected. After searching on Google, there were many questions about this issue, but few answers. Most responses suggested enabling JavaScript in IE, which obviously didn't make sense since the webpage could already be opened. The problem of "To access this page, your browser needs to support JavaScript" often appears in search engine snapshots like Baidu or Google. After much research, I concluded that the server's CC attack prevention feature was enabled, and any non-human visit would return this message.
CC Attack: The attacker uses a high-traffic website to attack a smaller website or virtual host. For example, if sina adds <iframe src=http://www.qzhen.com border=0 width=0 height=0></iframe> to its homepage — perhaps 10 or 100 times more — then if 1 million people visit sina in a day, it would be equivalent to 10 million visits to your homepage. A regular server wouldn't be able to handle it. CC tools are simpler than DDOS and can sometimes be more effective due to the authenticity of the traffic, making it difficult to defend against physically. However, there is one fatal flaw: HTTP_REFERER. By judging the referral source, you can block the attack source and take appropriate action.