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Hidden spammy links injected into web pages on legitimate websites is quite a widespread type of hacker attacks. These parasites try to suck all the “PageRank juice” out of any website they manage to break into and put their shady web pages high in search results.
There are many ways hackers can inject links. They can insert them as plain HTML (will work on most sites) or as an encrypted PHP code (the files should be processed as PHP). Hackers can even use SQL injection on database-driven sites that don’t properly sanitize user input.
Decoupling code from data
Sometimes hackers decouple code from data and inject only some PHP instructions that load spammy links from a standalone file. This makes the construction more flexible since they can simply change the content of that single file whenever they decide to promote a new set of links – no need to update every infected file on a site.
In this post, I’ll show a even more clever way of decoupling code from data.