This is just horrible.
Still, kind of scary to see. It's like a listening netcat piping to bash in a loop. Sure there should be a firewall in front...
Leaving this open is just hoping someone runs "rm -rf /"
https://github.com/search?utf8=%E2%9C%93&q=include%28%24_GET...
There is a simple Google search that allows you to find thousands of websites that do this. Which I won't put since it essential gives you a list of websites ripe for take over.
SQL.exec($_GET['sql'])
Was used for support to be able to access customer data to be able to reproduce bugs, etc.So if your PHP file executes eval($_GET['code']), then arbitrary folks can submit whatever code they want as a parameter -- as in /index.php?code=blah -- and have your webserver run it for them.
[1] http://php.net/manual/en/function.eval.php [2] http://php.net/manual/en/reserved.variables.get.php
Although it seems like most hits are from PHP Vulnerability Hunter -- an automated whitebox fuzz testing tool capable of detected several classes of vulnerabilities in PHP web applications.