This indicates a possible exploitation of a PHP "remote file inclusion" vulnerability. Attackers usually spread malicious links or insert malicious links into web pages on legitimate websites. When victims visit these links, their web browsers are redirected to attackers-controlled web pages.
Any website that runs any PHP software which allows "remote file inclusion" is vulnerable.
Attacker can use this method to redirect victims to malicious websites and infect victims' computers.
Please check if your web browser is redirected to malicious websites.