This indicates a possible attempt to exploit a PHP "remote file inclusion" vulnerability.
The vulnerability may allow remote attackers to spread malicious links or insert malicious links into web pages on legitimate websites. When victims visit these links, their web browsers are redirected to attacker controlled web pages.
Any website that runs any PHP software which allows "remote file inclusion" is vulnerable.
System Compromise: Remote attackers can redirect victims to malicious websites and infect their computers.
Please check whether your web browser has been redirected to an unknown website.