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Recently I analyzed a porn doorway script and found an interesting way to obfuscate an IP address there.

As you know, IPv4 addresses consist of 4 bytes (values 0-255) separated by dots, e.g.

In the above code, you can see that each byte of the IP address $adr is represented by a string of dots, where the number of dots in the string is the byte value.

This give us the following IP address: 173 .236 .65 .24, which is used to generate a redirect URL for the doorway visitors:

header("Location: hxxp://$ard/input/?mark=20151119-$s");

In our case, the final redirect URL was hxxp://173 . 236 . 65 . 24/input/?mark=20151119-<hacked-site.com>/azq9mzo3v

This code was found in thousands of .php doorway files created by the attackers. This is the sort of a hack that may cause troubles even after you have completely cleaned your site. You can read about such scenarios on our blog. To prevent Googlebot from indexing and re-indexing tons of pages that shouldn't have been there in the first place, it may be a good idea to close spammy directories on your server with robots.txt directives.

If you find something like this on your server, it's only a tip of an iceberg. To stop the hackers, you need also to find and close all security holes (including the backdoors that they uploaded to your site). If you need a professional help in malware cleanup and site protection, please check our Website AntiVirus service.