Unknown Meta Tag In All Responses In Laravel

I am getting an unknown response in all requests to a laravel 5.3 app. eg if i make an ajax call that expects json response. i get that json response but with an unwanted meta tag. due to which i am not able to decode json response. this is what i get when i make an ajax call to get json response.

<meta name="verify-admitad" content="8e6063a16f" /> {'some valid json'}

also status code is 200

i get this meta tag not only in ajax but also with normal request.

i figured out what was going on that meta tag was added at the top of the index.php file, and hence i was getting it in all requests. But now the question is where did it came from, did i was hacked. i am using hostgator for webhosting. can anyone suggests me how to avoid this in future.